Just from what I've researched so far.
As i'm not an engineer or electrician technical answer you wont get from me.
I've just seen a LOT of DIY builds with reasonable accuracy.

When i see parts i see things that i've seen it in or used often far from the field that i'm researching.
Example would be when i looked at my mates WP site and had to learn the tinyest amount about mild steel.

With this i know that for £20 i can get 6m of equal angle mild steel at 3 or 4mm thickness.
This is made straight and is strong combined with V Groove bearing with a 2.5mm Drop (groove) should work as the roller bed worked in the car garage i once worked in.

Belt or Chain above Ball n Screw so i've been told, so i'm going with it for now.

I have 3 steppers controlled with Gcode and a universal gcode streamer.
Software Easel.com
Simple Pi or Ardunio Set up
Motor Drivers Power supply with plenty of Ampage.