Warco WM16 Conversion

[m_c]

1) Looks like a reasonable kit for starting with, and should be more than up to the job you're asking.

2 & 3) Certainly on the z-axis, I'd be considering a reduction drive, or an extra counterbalance to reduce the weight the stepper is having to lift.
You need to allow for the loads being greater when cutting, and also as you're running the normal leadscrews with their reduced effiency compared with ball screws, it may be wise to run reduction on all axis.

4) Bipolar parallel provides the best match to the drives.

5) I've seen plenty builds where motors are connected via connectors. Main thing is you use good quality ones, that lock in with a high enough rating, and make sure you never unplug them with the drivers powered on (doing so is likely to lead to the drives becoming an expensive paperweight!)

6) Probably best to start a thread in the CAD & Cam Software forum, as I have no idea about linux!