I think 3 is meant to read "good tolerances on components" I'm not 100% sure Id agree although it is helpful. 0.1% parts dont make a piece of hi-fi gear, a good design does. Food for thought: 10% parts are matched better than most analog volume controls. Id certainly do better when its easy enough, but dont get hung up on this one.
I'd disagree with PCB's. They are helpful, but totally unnecessary for many designs. If you cant make a PCB yourself you are limiting yourself to "stuff other people like" and other peoples' decisions about how an amp should be built. If you can make a PCB you are officially AWESOME. There is a LOT of very good sound to be found in amps that people dont commonly build because nobody on head-fi point-to-points anymore.
Good basic design is open to a lot of interpretation. SS with more than 40db of global feedback & only a little distortion VS Tubes with no global feedback for example... both can sound VERY nice.
Ooh, and DIY gear can most definitely be hi-fi. Quite a few hi-fi companies were started by DIYers who liked to tinker, tried something unusual or unconventional, and found something neat.