You seriously don't want to get married, have children or even cohabitate in the current political/legal climate.
Apart from that you want to chill. It's too bad you still have work to do so you lose some years, but your teens/twenties should be used to build your own life around yourself. If you date in that age, then you fall in love... and then you do something stupid like get married and you have no clue how to live on your own.
To what extent are you self-aware? If you ask a girl out, do you know when you are being weird or creepy? If you are aware of it, then you are halfway there and it just takes some practice to stop being nervous around girls. At a certain point you just start guessing what their next reply is and things become annoying 98% of the time rather than so exciting you end up looking weird.
Appearance is probably the most straightforward to fix. However, it's hard to tell exactly how bad this is hurting your chances without specific information like bodyfat% (only really reliable are calipers and even that can be messed up). Losing weight and building some muscle can only help. It's also unhealthy to keep this up.
To lose weight while keeping muscle intact you need to lift (There's a book out called Starting Strength, 3x5 Squats/Bench/Deadlift and Squats/Press/Pull Ups alternated 3x per week with weight added each workout, pretty simple) and 1.6g protein per kg of bodyweight. To lose weight you need to take in less calories then you burn. Calculate how many calories you are currently eating. I would start off at 2000 calories and a healthier meal plan with enough protein and see how it goes. Unless you are currently eating like 5000, in that case even 2500 can make you lose a lot of weight in the beginning.
As for the types of girls you like... go where those girls are and... check out what kind of guys they are walking next to. Yea sometimes it might be just a friend or even a brother, but you'll be able to get some sort of a pattern going. Goth chicks go for tall lanky dudes, in my experience. Nerd girls... uhhh... I've seen them with other nerds... but also near metal looking dudes. Both of the gf's I had who might be what you consider that type were into metal heads, but there's also the ones that are like rocket engineers that want a perfectly chiseled businessman. Just check what the situation is in your area.
If you are the right type and you don't look like grampa you can get any girl of legal age at 30, being balding might mean that you are going to have to adjust that upwards to maybe 25. 30 is borderline not-creepy for 18 year olds
Hopefully you are lucky and you actually got a perfect face underneath that fat.
All that aside though, if you got a bad face you are just not going to ever do well with women. Who cares anyway? You should chill more and learn that you don't need a woman. That'll also help you appear less weird and creepy. It's not like the perfect little romance you have in your head. It's messy, usually expensive and always annoying in one way or another. Doesn't mean it can't be great, but you are totally undervaluing the benefits of being on your own.