I've wired basses like this for guys. Pretty much any pre will do. You should ask your tech to use trimpots, mounted just under the electronics cover. It's pretty easy to mount them on a piece of circuit board and make a little bracket to screw to the side of the control cavity. These are trimpots:
They act just like regular pots, but they're really tiny and are operated with a small screw driver. You can then drill a hole in the electronics cover just above each one so you can still adjust them if you need. Just throw a little phillips head in your gig bag.
I wouldn't bother with a volume control. If you do a gig where you really need to adjust volume, you simply use a volume pedal.