#1
So I have been wanting to customize my fender strat. basically I want a slanted humbucker. Is it worth it and is it hard?
#2
fender or squier?

Squier yes,
Fender, its up to you, I wouldn't cause it would ruin its resale value etc.

What you have to do is route the body for a slanted HB and then either make a pickguard or get one custom made for you so that it fits