I see.... well I am learning something here too...

I have a set of MT3 collets rather than a collet chuck. I can see a collet chuck would be easier to switch tools with and could help avoid moving the head up n down. Have you used the collet chuck for drilling, and if not, why not? My 16mm drill chuck is huge.. I am thinking of getting a 10mm one to be of a similar size (vertically) to the boring head so avoiding head movements when switching between them. But of course you wouldnt use a boring head on CNC, you'd use a small mill on a circular cutting path instead, although deep bores might be tricky.

What happens if the part has no through holes to bolt it down with, or are these in the excess? Presumably the reason for the standoffs is to allow you to machine around the outside and inside in one operation (and to space it off the bed? - or do you use a sacrificial?)