#1
be open minded with this question but I'm getting pretty decent at solo'ing and I feel a lot more comfortable having my 1-4 fingers flat when on frets kind of like how your ring finger is on a A Minor barre chord. Is it all a matter of preference or am I gonna catch heat for not having the arch going on?
#2
Whatever works for you, I guess, but flat fingers will eventually run into problems with a lot of the more complicated solos. It'll also cause pain in your hand over time, particularly in your palm.

I've always gone with the arch.
#3
You definitely want to go with the arch. The more nimble you need to be, the more the flat fingers are going to slow you down. Even if it doesn't seem to be holding you up now, the way you're practicing now is building the foundation for the guitarist you are going to be in 5 years.