As a Architectural Designer, the typical 4-6" slab is adequate for most garage floors.
But the slab is only a flat working 'cover' in effect. That is, it's not to be confused with and actual load bearing part of a concrete floor system. Those are the footings. The wire mesh is to give the slab...
Is that the only 220volt machine you're using or do you have more?
If so then you don't necessarily need the sub panel if there are spots left on the main panel.
I had over half of my 200 amp panel dedicated to electric baseboard heat which I changed to pellet heat so it freed up a lot of space...