"won't grow much"...mmm I'm wondering about that. If you can find an example of someone Squatting 300lbs or more with slender waist lol.
According to
wikipedia Jay Cutler has a waist of 34inch/86cm. I'm sure he can squat that 300lbs, even though he is not famous for squatting ^^. Anyhow, my waist is 84cm. And I'm sure I cant squat as much as he can. Even though my estimated 1RM is about 300lbs.
I would not expect for myself to get a much bigger waist than Jay, who trains exclusively for size/looks - even though I'm taller than he is.
Now it depends on what you define as slender

. If you would see my in real life, I could fit in that definition of some people - not sure about yours.
The other body parts is a different story.
Regarding pants

: I myself was in need to buy new pants recently (because of squats I guess

). My old pants stop fitting at my thighs. They felt compressed

. And I will soon have the same "problem" with the thighs again I guess.
PS: You should change your profile pic - this is why I came up with "dont worry". In your progress diary the pictures look different

. Congratulations btw ^^.
Something's wrong with my profile pics, the old ones seems to get error displaying so I deleted, and whichever new one I upload also appear as an X.