I just finished building my second one today, it's by far the best route to go in my opinion (mainly because I'm a tinkerer)
I'd suggest the Phoenix Trinity grip if you're okay with the wait time, I waited about a month for the super aggressive stainless steel one and man is it awesome! That aside, I'd suggest the CK arms frames, they're the same ones made by freedom gunlocks and they've got a different metal that is less prone to cracking (at least that's what I've read). Slides can be had from speed shooters or shooters connection. I like the CK arms ones personally. As for barrel, I highly suggest the Kart EZ fit barrel. Get the barrel fitting kit and possibly a few different bushing cause the one I got from them definitely didn't work.
Aside from that, I'd recommend getting the Jerry Kuhnhausen books if you don't have them already. They are a fountain of information and by far the best reference for if (or when) shit hits the fan. Go slow and always measure everything multiple times. Remember you can always take more off, it's not necessarily easier to put more on.