If you only plan on one I don't think it's worth the time or the investment in tools.
I would just buy one and be done, it's what I did.
If you're wanting to build multiple riffles then yeah, get the tools.
I would stick with 7.62 or 5.56, 5.45 is sweet but it's nowhere near as cheap as it used to be and a much better selection can be had in 5.56.
I second, or third? this. Just buy one premade. I have a bunch of fancy AR's, but I still think I like shooting my AK's more. Between my brother and I we have 5 of them. Even the Century builds (just looked up a bunch online for under $600 - I'm sure there's some cheaper locally – those used to be like $450-500 a couple years ago) are perfectly fine contrary to internet wisdom (if anything is majorly messed up they will fix it free of charge, just mail it to them from UPS like any other package - check your laws though, that's how it is in Pennsylvania at least).
If you want higher end I HIGHLY recommend an Arsenal - couple years ago they started doing more budget friendly models which start at a little under $900, and even those are still pretty choice (still AK's though so don't expect perfection on all the parts). But honestly, even my little 11" Century Draco underfolder SBR will still hit the 6" steel at 200 yards all day long, so it's not like you're gaining massive performance benefits when you go with Arsenal with the ranges these are meant to be used at. Definitely go stamped receiver over milled - the weight difference isn't worth it for milled - they're friggin heavy tanks.
I would not get it in anything other than 7.62x39 though - that's what a traditional AK is supposed to be in my mind. They are extremely smooth shooting (especially with a good brake), even compared to 5.56. 7.62 Ammo is still relatively cheap too (can pickup a 1k case at gun shows for $220, maybe even $180-200 out the door if you're still lucky). 7.62 mags are dirt cheap and you really can't kill them (I have about 35 from all different countries...think the only stinker mag was a plastic 'range only' type I picked up for $8 - all others are steel and/or bakelite and/or circle 10 bulgarian and indestructible pretty much). Some great aftermarket triggers out now for AK's too - they almost give my Geissele SSA-E's a run for their money (ok, almost, but still SUPER smooth AK triggers are an easy drop-in anymore).
