Bearing in mind that I'm a really unaccomplished model builder and know nothing about metalworking, putting together the pieces was not difficult at all, but the mechanisms of the barrel don't work on my gun for the most part. The trigger and hammer work, but after spending too much time fiddling with the barrel lock, I ended up gluing the barrel in place. Otherwise, it kept falling open of its own volition. I figured that it didn't open in the movie so I'm not really upset about losing that feature. The bolt works just fine.
The metal is very soft and the thin parts are prone to bending. On top of that some of the pre-drilled holes did not match with one another and the screws as well as I would have liked. You have to be careful putting the screws into the soft metal because if you go in crooked, you’ll forever ruin the screw hole. For the same reason, you don’t want to tighten and loosen the same screw too many times. But overall, I'm still thrilled with how the replica looks and feel and it's still a real bargain for the money.
It was not difficult to paint at all. Since I was going for the "weathered" look I just hit all the painted parts with some black Rust-oleum, let it dry, and rubbed the edges with steel wool. I rubbed a thin membrane of gun blue on most of the exposed metal and voila! You can't see in these pics, but the bullets are also sprayed with metallic brass paint.
I'm also going to be installing the LED's and battery, probably this weekend.
Thanks for all the comments!