Not much as much as you think, apart from the routers, computers and phone, the only other thing I can think of is the dishwasher because it's half-recent. And I suspect the new ones just include a cheap Android board.

> And re: your Android board: come back when your bricolage conforms to all kinds of requirements. Extended temperature range. Vibration. Electromagnetic compatibility (it‘s easy to accidentally broadcast in the naval emergency band). Etc. etc.

I've worked on a company which manufactured their own card, that is much harder to do by yourself than buying a board which has been produced at millions of units where they solved all those issues directly. You can't compete with that easily. We had at least 5 iterations to solve the magnetic and heat issues, all of that comes for free in a mass-produced board.