4" or 5". 4 jaw chuck for 7x12?

[petcnc]

Might want to consider the weight that will be hanging on the spindle bearings. Lot of metal in a 5"

You are right!
I forgot to mention that I have changed the chinese ball bearings to taper roller bearings. A pair of SKF 30206 taper roller bearings, at a cost of 25 Euros, significantly improved the performance of the lathe. I think they can handle much more metal than a 5" chuck.