I've built a few CNC routers from scratch but these are all full alloy builds using heavy extrusion, 6082 plate and HIWIN blocks / rails with ballscrew components. I have one large format machine with a 40W laser attached and that has been more useful than I ever thought possible. Plenty of small solid state options in the 2-6W range which would be a doddle to fit to one of the machines you posted.
Depending on what you are cutting, those look superb ways to enter basic CNC functionality. Can't help on the printed part mechanics of these projects but have enough time in the motor /electronics side of things if you want to pick my brains.
I've seen a fair few CNC builds that use essentially 3D printer control type boards but in my opinion a standard breakout board and Mach 3 or LinuxCNC would be a better route as there is a bigger base for support out there. That said, this may have evened out a bit since I last looked at it.
These guys used to be superb; https://www.aluminiumwarehouse.co.uk/
but about three months ago, itself about 24 hours before I put a large order in for my next build they upped their prices by about 30% and their customer service dipped a little - I suspect accountants were at play here but worth knowing about if you didn't already. They interestingly used to sell Irwin tools and clamps significantly less than anywhere else on the web but seemed to have dropped that as well.
Do check Ebay and the usual Chinese outlets such as Aliexpress for CNC linear guide ways as they are ridiculously inexpensive these days for low cost CNC builds. The 13"x12""x5" work envelope of the first example you posted wouldn't cost that much to achieve using off the shelf components. I appreciate the aspect of building yourself but do consider the options.
Lastly, I don't notice any limit switches on the posted machines, if they don't have this I would seriously consider fitting them - I'll wager that you will end up doing it anyway.