I got a pair of Frankensteins on Boxing day for pretty cheap (80$) and I sized down... However, the problem is that I need to hem a lot of it, but as of now, I just folded the denim inwards (since it looks weird if I flip it out when it isn't selvedged).
My question is, should I get it hemmed asap? and how would you measure the shrinkage after washing so that I don't hem too much?
As a general rule of thumb, it is best to get jeans to the length that you want them at ASAP once you know what that length is. The reason why is because if you wear them differently, you may create fades or creases in the legs now that you might not want later once the jeans are the right length.
From my experience, N&F only shrinks about an inch at most in the inseam after repeated washing, so if you give yourself an extra inch when hemming, you should be pretty safe.
How would skinny guys fit around the thighs if I size up 2-3? I usually wear a size 30 with slim straight jeans, and they fit me well enough that I don't need a belt.
They'll fit less tight in the thighs, which is nice IMO, but the waist will be so loose that the jeans will be falling down if you don't wear a belt.