LOL, no when I mean starting an OS from scratch I mean formatting a hard drive and installing the OS with the correct updated drivers. Writing code for an OS has nothing to do with being a service technician.

The reason I recommended PC's over iPod's is because where I was from, it was easy to find free or extremely cheap ($5 - $20) PC's that people were getting rid of either because they were broken or upgraded and wanted to get rid of it. When I first started doing stuff I didn't really "build" PC's, I modified old ones with new parts. I had a working computer and plugged in broken parts to find out which ones worked and which ones didn't. I really only worked with computers that I got for free because I wasn't trying to make any money.

I really don't have much advice if you want to go the iPod route. I think it will be much more difficult to find cheap or free parts. The parts also aren't really interchangeable which will make things more difficult, but idk I really haven't looked much. Post on Craig's list that your looking for old/broken iPods and see how many responses you get :)

An iFixit tour would be very boring. We are not a repair shop, we are a parts store, so we just have many shelves of parts and some testing stations.