I've seen that cd rom printer. Great concept, but proved completely impractical in operation.
Hot ends won't be from some random Chinese aliexpress seller. In fact I plan to avoid them as much as possible. I've never seen the hexagon before but seems interesting. Biggest impact though will be on the quality of the nozzle and heat break. I've been looking into some of the newer designs that have tried to integrate them all into one piece. Nothing truly impressive yet stands out for me.Also I have to weigh the pro's and cons of an none standarded hot end for people who are probably building there very first machine.
I've gotten a lot of printer rods over the last year. Almost all of them have been far better then anything I've seen out of DIY kits. I found a good way to test straightness of a rod, roll it on a big, thicker piece of glass. You can hear warped rods even if you can't see it in them. Gotta love physics. Also an indication of the quality is the consistency of the diameter. An 8mm rod is almost always 7.92. I'd love to see a 3D printer maker have that kind of consistency.
Your right aluminum is better then PCB. But I'm thinking if I can get a reliable PEI bed. Looking at the PEI sheets Prusa sells.
Yeah there is definitely a difference in quality in power supplies. I know what to look for. With the selection at Free Geek there is no reason to settle for junk.