Hi. I'm 20 years old. 5'1''-5'2"" depending on the day. My weight is in the double digits. Most of the family on my mom's side is short and/or skinny/slim. Not on T. I sometimes wear girls jeans or Rude skinny jeans for a better fit.
I'm not on T yet, but I'm worried about a lot of weight gain.
But I'm happy and pretty content with my size.

you won't get fat once you go on T unless you don't exercise, etc. the most you will notice is more muscle or easier to gain muscle i guess. so you will get more weight gain from muscle but not fat.

I don't find bigger guys hot at all, skinny/thin guys with a touch of nerd is more my go

Yes! Yes! Yes! Oh My Cuthlu Yes. There is nothing saying guys need to be versions of The Incredible Hulk. As long as you are in a healthy weight range and are healthy it is fine.

Plenty of nice skinny guys around. As long as you don't look gaunt or skeletal you'll be fine!