I've been trying to think of parts that can be ruined by rank amateurs. I guess there's a few, but so long as you use the correct tools and follow instructions, you'll be okay. If there are disappointments, it is likely to be a frustration with getting the adjustments right on. So do like I did my first couple of builds - do your best and then tote the bike to your friendly neighborhood SpiderMechanic for a checkout. Chances are he'll do some minor tweaking then say you did okay. After which you'll ride a LOT easier knowing that a pro screwed up too. [Err.. maybe I should re-state that.]

OTOH, I hope you are aware that "upgrading" is a money-losing proposition regardless of the required investment in DIY. You'd be better off buying a whole bike for the cost of the "upgrade". Then you can do your wrenching without having to worry about getting your ride back on the road so you can .. uh.. ride.