Whatever cnc project you take on for the first time, there is certainly a long learning curve. I agree that retro-fitting older machines has it's own difficulties. But, hooking up stepper motors, motion controllers and wiring electronics are challenges that can be overcome with research, patience and a little help from the forum. Building a precision machine base in your basement with nothing but a drill press is something else entirely.
I literally could not buy the iron for a diy project for the same cash as a used Industrial machine and creating precision flat rail mounting surfaces, if you don't already own a mill, is a hill many diy projects die on.
The way I see it, there is nothing wrong with giving yourself a head start where ready made used parts cost the same or less than a full diy option. You can spend months trying to figure out how to make a strong and stiff gantry with precision flat and parallel rail mounting surfaces, or snap up a sweet piece like this:
https://www.ebay.com/itm/Tru-Stone-1...QAAOSwD~Fb5lUL
It has precision flat surfaces, pre-drilled mounting holes and a ready cut groove so you can mount a ball screw on the back (protected from chips and sawdust). I just wish I would have seen something like before I started my project...
You could spend months trying to teach yourself to make a base with a harbor freight welder, or... snag one of the many precision bases being thrown away for pennies on the dollar:
https://www.ebay.com/itm/Newport-Dyn...4AAOSw0T9c1bs4