thats actually a nice technique but i imagine you have quite a bit more mass than me so idk what i should expect lol.
Yeah obviously, but I wasn't far off you at your age (bar quite a bit taller)
These are my suggestions

Opt for a slim fit shirt of a smaller size (stops the bunching as much)
Don't worry about arm length, if you're a true ectomorph you'll never get a right fit anyway - roll them always
Something tighter around the neck will make the world of difference, also shoulders should be narrower
Pants should be slim fit again, should be lower than they are from where i'm guessing your hips are