As far as the initial question goes, "do I tell them up front?" I have had a lot of experience with this over the 11 years I've been in the work force and I have a little I can give you to keep in mind, if you feel like listening.
1.) Need to know basis. The more of your private business you make public, the more you welcome prejudice. Tell your secrets and you roll the dice, basically.
2.) Use your best judgment on the "need" and ask a friend for help. When I say "need to know" you should understand when a manager actually does need to know or not. Just because you have limits doesn't mean it will be a problem for a specific job. That particular job... yeah, that would have been a 'need to know' but unfortunately it is also a legitimate reason for them to not hire you and you can't be upset and start making prejudice accusations because they didn't hire you for a job you were not fit for. Now, if you were doing a job that was more of a desk job and you had small problems here and there, just handle it until it becomes a problem. Then you tell someone.
3.) Don't lead with your disabilities. I can't stress this enough. When you interview, you are a salesman selling your time for their money. If you start off a sales pitch with all the things your product can't do, your customer will already have a reason not to buy before you give them the reason to buy. I always try to interview so that I make them want me bad before throwing in my disability.
4.) Choose your job wisely. Like I said in point 2, don't expect to be hired for a job you aren't going to be good at. I know how rough it can be but poorly suited jobs should be last on your list.
5.) We are promised two things: death and taxes. Following point 4, understand that no one owes you anything, they don't owe me anything, no one has to give anyone anything. I hate to sound bleak but hear me out, it goes deeper than it sounds. Once you understand this concept, truly, you will then be better at point 3! You need to learn that no one has to give you any job, you need to sell yourself better. And as stated in my analogy and point 4, you can't expect to be hired for a job that you aren't suited for.
6.) Be a worker, not a poster. It doesn't matter if you are gay, autistic, religious, political, furry or whatever... 99% of entry level positions do not want a poster child in their team representing their company. I understand the whole "be yourself" mantras but as it seems in your OP, that isn't working out for you so listen to someone who does this professionally. Leave yourself at home; leave your problems at home, your opinions, your sexuality, your religion, everything that is not needed to do the job well. They don't want someone who has a strong enough style that it may offend people, whatever that style may be. You become the worker they need and nothing more. These are entry level jobs, not dates or conventions; you aren't looking for a place to share your interests or personality with, you are looking for money.
7.) Understand your position in the interviews. Something that I have to tell everyone I teach about job interviews is that the interview goes both ways. They are finding things out about you (probably more than you realize) so you need to be doing the same thing. If you find out they don't like homosexuals, then don't tell them you are a homosexual. If you find out they are a liar, don't work for them because it will cause problems like you wouldn't believe. I could write a book on interview and managerial analysis so I'll spare you more examples. If you aren't good at this, practice. Getting a good job is hard and there are no handicaps for us regardless of what you think is "legally required."
8.) Written tests are the only time God wouldn't blame you for lying. I don't know if anyone told you this so I will make the point. If you take a personality test or morality test or anything like that, for the love of god choose the answer that they want to hear, not what you think or believe. We as aspies can rationalize things all day but you'd be surprised at the sneaky hidden meanings behind those tests that even we wouldn't have figured on our own. The first time you take them, do it online and with someone more knowledgeable sitting with you to play Devil's advocate. These questionnaires are a web of lies designed to find loopholes in your morality and character. I didn't say they were bad, but they are not what they appear to be. I have studied some on how they work and how companies really use them. We aspies are at an extreme disadvantage.
9.) Just because it's legal doesn't mean it'll happen. I understand that companies have to help with disabilities but there are a lot more details that don't come across on the passing info. You see, even if someone discriminated against you for your autism, there are no discrimination police and if there were, you would need proof. You also need to brush up on federal, state, county and city law because each level has it's own ability to supersede the others. For instance, the federal law may say that you have to be considered for a job and be accommodated but the state may say that you can be fired without reason, giving bosses the legal ability to terminate any candidate without serving discrimination up on a convenient silver platter for you to use against them. Also, this means that there are laws that allow small and large companies to get around what you may think is your "right." For instance, I used to work at UPS and my driver used to pick on me and cause me grief. At one point he caused me to be injured and I had to go to the doctor. Instead of getting worker's comp, they gave all these legal technicalities about going through the wrong channels for procedure of seeing a doctor and thus making my diagnosis unrecognizable for workers comp. If I wanted compensation I needed to go through more paperwork but before I could do that, they simply fired me saying I wasn't able to do my job anymore. So you see, legal obligation is not your weapon, it's theirs. You probably aren't a lawyer, but most people who have businesses have lawyers on call who host meetings for the staff. And what are you going to do about it, really? You can't hire a lawyer to sue over an unprovable accusation and even if they did, the company has better lawyers than what you can afford. After all, you are unemployed and they are a profitable business. You have to know your place in that legal battle.
10.) Use size to your advantage. If you are having a hard time with entry level positions then shoot for a smaller business. Point 9 is long, I know, but that's because it deals with legalities. In contrast you will find that "mom & pop" shops find such nonsense too complicated and they play by ear. If you are nice and friendly and can help them with anything they need, you can get a job with no fuss. But lead with your autism or sexual life and you won't get hired anywhere.
11.) Never use a card. Much like point 6, this deals more with the rejection side. Wether you are turned down, fired or something happens at the job on any given day, if you use the "I'm gay" or "I'm autistic" or "I'm of blank race" card, you lose. Simple as that, you just lost the altercation and offered yourself up for being fired. Forget about what you think is right or wrong because you can't force your beliefs on them any more than they can on you (as well as it should be for a free country). Simply put: It's not your company. The second you instigate a segregation, you will segregate yourself away from the people who signs your paycheck. Doesn't even matter if your boss is gay too. Professionally, they should be more obligated to keeping things running smoothly and as soon as someone starts throwing accusations around, that employee separates themselves and stands out like a sore thumb. Understand that playing a "card" of any kind is very much an accusation and wether you are right or wrong, I urge you to be very cautious and very withdrawn about doing so. Even if you think no one will hear/read it.
12.) Don't post online. This also can't be stressed enough. If a stranger like me can read it, they can read it. Don't forget that there are plenty of hours in the day and many people who can be called between the first time you give them your information to the time you get your paycheck. Your OP (original post) wasn't bad, it is very warranted and I personally have no problem with it but it goes back to my bumper sticker analogy and takes a dark spin. Even though you may be asking for reasonable advice on a site like this, or any other, someone may find it and use it against you without you knowing. This is most important with your facebook and any other profile you have. I can't be certain but I have had threats from some of my more mouthy bosses that suggest that your information can be gotten easily with the right knowhow and the information you put on your job application. Remember, job applications ask you for everything, even your social security number. You better make sure your nose is clean.
I know it's a lot. I'm sorry. But this is a very complex situation and I'll bet SocOfAutism may agree that these things aren't so simple. Please know that none of this is meant to be mean or accusing or personal. However, you ask a good and reasonable question and I answer to the best of my ability. I do hope it is informative and helps. Again, I may have an idea for a good job if you want to hear it. Let me know if you have any questions about what I said and I wish you the best of luck! Keep your spirits up!