Originally Posted by
Kayce
fork and headset are required before you get a stem, bars, and a front wheel
Correct.
BB is required before you get the cranks, chainring, and chain
Incorrect. BB and crankset should be purchased at the same time, because the crank will dictate BB spindle length.
rear wheel is required before a cog and lockring or freewheel.
seat post is required before you get a seat
All correct.
To the OP: It generally doesn't matter what parts you buy first. You need them all before you can start riding it. Well, I suppose you can get away without a seat and seatpost, but I don't think it would be a fun ride. I'd start with a set of wheels, because that will likely be your biggest expense.