I've built this machine 100 different times in my head!!!

[JAZZCNC]

Like jonathan it's nice to see someone who's actually done the leg work and payed attention. . 10/10. . Big respect. .

Agree with Jonathan on every thing he's said except not using the Ecocast.! Even thou you will machine the bearing mounts etc unless you surface and make parallel both surfaces your still going to have troubles and in-accurecy. The problem comes from the cheaper plate not being uniform thickness so you can't be sure it's the same thickness (Or flat) all along it's length. This means buying much thicker than needed so it can be surfaced and still have the required thickness to be strong.
I used to do just this but since the Ecocast has been easily available in small qty then I don't bother any more and it cuts out some of the work involved and makes things that bit easier.

To be honest the 20mm plate is still fine regards strength even with the neccesary slots cut, I've made several with 19mm 6082 and slots etc and they are more than strong enough for even the most demanding jobs.! (Within reason) See pics of what you may have seen before just not striped down like these.?
(obviously more thickness will be stronger but not 20mm gets the job done.!!)

The only other point I will mention is the belt setup and the lack of protection from chips etc.!!
You probably know my machine use's this setup and I'm guilty of not covering the belts and while it's never been a problem, other than grabbing my teashirt a few times and trying to eat me, I would still advise you to cover them up before using the machine.! . . .I'm pretty sure the constant pounding from chips etc has or will shorten the belts life so worth doing before using the machine otherwise like me you'll never do it after machines put to work.!!

Anyway great work and can't wait to see it turn into reality. . .