Possibly the single biggest build issue is bottom bracket installation. Fork lower crown is next but as you state you've already installed the brakes I'll assume the fork is installed with headset, etc...

If the bottom bracket is BSA threaded then installation is easy. If press in, maybe a trip to an LBS to get it installed would be cheaper then buying a Park press tool and parts, or cobbling together a home made press.

Then the rest of it is easy. Ditto the idea of a few stems, or mail order a few different sizes and then return what doesn't fit.

I'm partial to Ritchey aluminum stems, bars and seatposts. Nicely built, good looking and functional. I'm a Clyde so don't try to save weight on these items with carbon.