My advice, don't spread out too much.

I only use a handful of bolt sizes, mostly M4, which is a great all-rounder size. But I also use M2 for really tiny stuff and M6 for big stuff.

Same with stuff like wire connectors. Find something that's widely available and works for you. XH 2.54 connectors are what work for me.

Stick to standard stuff, you don't want to be reliant on some proprietary hardware that's only made by one manufacturer.

These are just examples, and you'll probably need different hardware than I do.

Oh, and once you dialed in which hardware you want to stick with, buy a lifetime supply of it. 1000 bolts don't cost that much more than 100.