Bearings: Ok, thanks for the info - I'll continue to give those a miss.
Mounts: Sounds reasonable.
Stiffness: Understood - I wouldn't say Mori-Seki doing something one way is any reason to copy, as the relevance of their reasoning is unknown. Also I'm not sure my calculation in the previous post is any good, as the bearings are close they probably can't reasonably be considered as points, plus I ignored the position of the ballnut.
P.S: See here, from page 53.