#1
And Im just wondering... it looks pretty even but is there a way to check for sure that its perfectly flat, and that the left and right sides are the same height? Is it merely trial and error a little bit at a time?

Its a strat floating trem btw
#2
The pretty much only and best way is to check with your eyes. Look to see if it's level. you could use a spirit level and ruler if you're picky though...