As for that screw on the table adjust (Z)............. I checked mine, and it is 5/8", 16 inches overall length.
The length is all used when the table is fully up. You might not do that very much, but when you need to, the capability is there. Yes, you will need to have some significant space below the mill for that screw to retract into when the table is down low.
The screw that I do not like, is the table longitudinal screw. On mine, the screw is several inches short of the end of the table, and as a result, I have a line 2 or 3 inches short of the end which is the last place that can go under the spindle before the table stops moving because the screw has come out of the nut.
I intend to make a longer screw so that I can use the entire left end of the table. There is already a several inch space at the right end of the table which is not usable except for clamping, because the bracket runs into the knee. I can't afford to lose those inches at both ends. (I still wish I had one of the units with the long table, which was a crazy length, I forget if it was 24 inches or 36 inches. That could be very handy, but might be a bit floppy.)