The first kit I built was an FAL. I haven't done an AK yet but from what I know the FAL is a piece of cake compared to an AK. There is no riveting. Headspacing is not easy, but it's not an exercise in frustration either. With the FAL it is the upper receiver that is the serial numbered part, not the lower. The only tricky part of the build is timing the barrel to the receiver and that's not difficult, just tricky. IMHO the only receivers to buy are made by DSA, Dan Coonan, and Imbel. You will not have good chances of an easy build if you go with a $129 FAC special. You can buy from FAC, but get their Imbel or Dan Coonan receiver for about $200. Of equal quality is the DSA receivers but they usually run $350 on up - not worth it in my opinion. Receivers to generally stay away from are Century and Enterprise. Don't even think about buying an 80% FAL receiver unless you have a good quality industrial mill at your disposal and you are an expert at using it. Just get a Dan Coonan upper and be done with it.
If I was to build another FAL I would buy an Imbel kit that needs to be refinished and a Dan Coonan upper receiver with FSE US compliant parts. Build it in an afternoon and either send it out to be reparked or do it myself. Hell just spray paint it black, it's all good. :rockin:
On a scale of 1 to 10 with 10 being the most difficult, I'd give it about a 3. The only special tool that you really need is the receiver wrench. You can find them used or new for $35-50. I just borrowed one for my build. Oh yeah, don't forget headspace guages, but that's important for any rifle you build.
Pretty much all your questions can be answered at
www.falfiles.com. Good bunch of people over there although the site is starting to get kinda big.