Grrrrr...just realized I have to buy barrel adjusters for my DR cables as I don't recall them coming with the groupset. Yet more $

Punt. I do not use barrel adjusters. You don't need one for the RD (it has its own adjustment). The FD is so crude, no need there. And, my brakes don't need them.

Not sure if this has been covered, but biggest warning for a home mechanic should be one of safety. There are ways a bike can be put together that appears to work and appears correct, but is wrong and can lead to a crash. Not correctly preloading the steerer components with a star nut and cap prior to torqueing down the stem, comes to mind. There are probably others. It all looks fine and it rides fine for a while, then you hit a pothole and handlebars come off.....

That could be the start of a great top home mechanics tips thread. For example, I learned the hard way that you should use Shimano's connector pin on Shimano chains. (Back when I last replaced a chain, there were no special "connector pins.") Oh yeah, and Shimano chains are unidirectional; I overlooked that too. And, never build a bike while drinking. I can guarantee that your work product after a couple bottles of red wine will mess up your next ride.

Hah - I sort of unintentionally did that - my 6 yr old daughter literally just learned to ride a bike and graduated enough to have me ride slowly next to her. My half-built bike wasn't even in riding shape, so I slapped it together and barely had the handlebars on. Fortunately we were going walking speed, since after about 15 feet, I moved my hands to the drops and the whole thing rotated downwards and I almost faceplanted. Doh.

At the same time, I'll add i've been surprised with how hard it is to really make your bike a deathmachine by accident. Brakes are really hard to screw up even if you have no idea what you're doing, and once the wheels are on, it kinda goes by itself. If it weren't for derailleurs, the bike would barely need any adjusting at all.

Metal dental picks can be useful for guiding cable housing and cables when there isn't an internal routing system already in place.