The machine on youtube is very basic in its design with bearing running on what looks like steel box section. This wont give you high accuracy. the box section wont be perfect for starters and also with bearings and running surfaces you tend to get crap between them and this gives problems. What you end up with is stuff ground into the running surface and this makes the bearing jump or stick when it tries to pass over it, I have seen this happen many times on the profiling machine I work on, you need to keep them very clean. Also if you want to cut ali I think the design would be too weak for it unless you took very light cuts. I think it would need some serious beefing up. Have a look through the forum builds and Im sure you will find something there to suit your needs that you can copy and modify to suit. Both accuracy and speed are obtainable relatively cheaply and stepper motors will suit your needs nicely when added to some linear bearing and slides and some ballscrews. Servos are better but cost loads more and the controller for them would also be more expensive. I use USBCNC myself and I like it but there are others out there for you to try. As for PSUs there are good one and bad ones. Buy a decent quality one is my advice.
Apart from that welcome to the forum.

Ian