The biggest question in considering a first gun is this: what type of play are you going to be doing mostly?
There's guns that are better suited for each type of play, but since you're new, you might want to get one that can pull double duty decently. Your best bet would be something like a G&G Combat Machine (something like this:
http://www.evike.com/product_info.php?cPath=21_44_218&products_id=34900). It's short enough for indoors, but but can get *decent* range stock. The only problem with the CMs is the untreated aluminum inner barrel and the buffer tube screw not liking to stay in sometimes. Other than that, it's a good gun to start out with and can give you something to build on when you get some play time under your belt. Don't forget to get a battery, a smart charger, and some eye and face pro (a paintball mask will work).
If you're stuck on the UMP style gun, don't go for the "Umarex". Bad plastic, bad mags, cheap overall construction, ect. make it a piece of junk. Go for a G&G UMG instead. Get a hold of spazz, he has one for sale right now (or did last time I checked).
Other than that, welcome.
