I am about to start my first (AK) build myself, and like you my 1st project is an undefolder. The Candyman gave you some solid advise, and you will no doubt hear other people tell you the same thing: Start with a 100% receiver for your fist build, save the flats for later.
Like you I have spent quite a bit of time reading up and prepping for this build, studying on what to get and what not to do. I have learned to heed the advice of those here who have several builds under their belt. They are trying to save you a lot of grief by suggesting a 100% build.
100% isn't really finished. You will still have to line up and cut out the holes for both your front and rear trunions as most receivers I've seen were still missing these holes. Since they are already bent, you won't have any choice but to cut these on a finished frame.
It'll take some patience for sure. If it is your first gun build it's hard to estimate the difficulty of the build before starting. What might look to be the easiest thing to do might turn out to be a real pain, but on the other hand that one thing that you worry about the most just may turn out to be the easiest,