Hi, a bit of advice.

I see sth strange in this machine. May be i am wrong, but before buying and spending and cutting material, better do a continuity check. Element by element the way you will mount it together and check if thats possible and the difficulties.
I do that with whatever i build and in spite of that some times is difficult in real life to mount things together, there was an element in my first machine that cleared mere 1-2mm or it would not enter. Even that i have checked that 10 times .So dont use just copy paste, Hi but move the elements as they will be moved in real life.

My rule of a thumb is to leave clearance holes at least 1.5mm bigger in diameter, better 2mm. Cause the paint, the welding, etc... And when you weld, aim at precision, dont be in a rush. I have welded 1 meter machine under 1mm precision and 3 meter machine around 1mm. Its not a joke. And it was one of the first thing i welded. By the way 250A mig is best for home fabrication and costs about 350euro on ebay. Later when you can could change gun and cable with a brand one. Thats what i did.

Buy more material and use extra cut to size pieces as hard stops so you could achieve precision mounting. later you would use them for sth. And steel is cheap.

You need light preload, not 0 preload for the bearing blocks. Wider block serve nothing more than easier to mount usually for the gantry legs. On Z almost always the normal blocks are a must. Make sure you buy the long carriages.