Hi CNCRY,

Welcome to the forum!

Usual advice is to hold off on further purchases until you've got the design finalised and pretty confident about each electronic component - changes upstream can irritatingly change what you need on the mechanicals, and electronics have a way of updating while you're building, so best to buy once when you need it rather than in advance, so you've got the right idea there.

I suggest you read through the build log section of the forum; you should be able to look at the 3D Tek design and notice where they've done the right thing and where they've skimped. You've already identified that ballscrews are a more appropriate drive option for example - but there are a few design choices about the Z axis that I wouldn't emulate.

Regards your rails and screws choice, the rails seem appropriate, the screws are about right, but in this size I'd also consider 16mm screws and 10mm pitch options, but all depends on if you want to use pulleys. There are a few calculations you can do to help you determine whats best for your use, but you'll pick this up in the build logs.

You're correct that the AXBB-E has a breakout board built in and seems to get a good rep (I haven't got one!), but also compare against other options such as built-in controllers and say UC400eth with a cheap breakout or expensive breakout. Generally I'd say stick with Ethernet based controllers, unless you're going down the LinuxCNC route.

Voltage and PSU specs are again very common topics in the build logs so I won't delve into it here (but bookmark threads and page numbers when you find these things!!). Generally unregulated PSUs are preferred, a lot of users build their own, or purchase AC drives so you only need a toroidal.

Hope that helps!