Are you going to build from a fully machined and riveted receiver or are you a fairly skilled machinest with solid riveting skills? (blank receiver vs. receiver with trunnions already riveted in) The rivets on the stamped receiver will be one of the biggest challenges from that starting point. A milled receiver is a different type of build with the biggest challenge being the barrel pressing, which has to be done on both milled and stamped receivers. Getting a quality surplus de-milled kit with the barrel already populated with the FSB, GB, and RSB would be a plus for not having to make sure of no problems with sight cant, etc.
Also, finding quality kits with the original barrels is a "bit" harder to do but worth it. I have no idea for recommendations on aftermarket, American-made barrels. I was fortunate enough to find all my kits a long time ago with the original barrels still intact.
When you're looking through kits, some of the older Hungarian kits came with threaded barrels. You may want to avoid that because it restricts you to milled-threaded receivers only, which you then get into barrel "timing" issues. I'm sure you're already familiar with these characteristics.
Polish PMKMS kits were excellent kits. Russian kits of any usable quality/ matching SN's are pretty much non-existant nowadays. ROMY G kits were fairly plentiful for a while. I haven't seen any for a while, but there were some nice Hungarian SA-85M kits going around in nice condition. Make sure your kit is as complete as possible. All-matching SN's are a plus. (Original barrels with original matching front trunnions pretty much guarantees a good fit with close to correct headspace on first try assembly) As always, be sure to check your headspace.
If you're going the stamped receiver route, there are some companies that offer matching your kit's SN with the receiver and also using the kit's country of origin markings. (Hungarian, Polish, Romanian, etc.) If you find a nice matching kit, it's worth the extra money to make the whole rifle matching. (IMO)
Kits will range from virgin kits, like this Bulgarian AK-MUS 7.62x39 kit...
To the surplus demilled kits like this Hungarian AMMS kit with the barrel already populated...
And the Polish PMKMS kit (like-new condition)...
To the Polish PMKMS kit (used-VG Condition)...
Good luck! Looking forward to seeing your progress!
firstchoice