I would choose your drivetrain sooner than later. Get the appropriate bottom bracket and crankset and the necessary tools, and also get the matching cassette and derailleurs first. Installing them is SUPER easy and quick, and then you can put the wheels and chain on and you'll feel like you practically have a bike already.

It isn't all that hard to build a bike, and even if you're a noob it won't take you all winter. If I had all the parts on hand I could do a frame-up build in just a couple hours. Wrapping the bars and running the cables takes longer than pretty much anything else lol.