No one mentioned, but maybe you already realize...you will need to cut/remove some of the stock fender tubs. You can easily cut them with a box cutter, dremel tool or similiar just make sure you don't cut any wires or harnesses attached to them. A lot of guys totally remove them, personally I salvaged as much as I could. I only removed the outer half, saving me from having to relocate a bunch of wires. Once the glass was on, I made a template, and used aluminum flashing to give the fenderwell a nice, clean look underneith.
As for trimming and sanding, I would use a dremel with small cut off wheel, and very fine sanding disc. You could also use a grinder with same, but it's overkill and unless your confident with your skills you could damage the fiberglass.
I never had any problems with my front glass (no trimming req'd) nor with the two buddies when I helped install theirs. It is usually the rear skins that will need the work. Their should be indentations in the fiberglass mold along the top, and side where your holes will need to be drilled (at least mine had)
I re-used all my stock trim, just cut it to fit the fiberglass fenders and re-attached once the glass was on. Alignment is the hardest part, the trick is not to tighten the bolts all the way down. Close the hood...check alignment...make adjustments...tighten some more. Continue till satisfied.
Oh and do all your drilling, sanding, and such first. Then take them off and go drop them off at your local auto paint shop. Mine front glass was $80 to get painted.
Good luck, J.