Yes the train crew have always been Bletchley based drivers and conductors who also work mainline services. There's no specific branch line pool, infact there were some crew diagrams which had mainline and Marston Vale work in the same shift.
The maintenance staff have all been recruited from scratch for Bletchley TMD it seems, a few months ago WMT had job adverts on their website for technicians and supervisors at Bletchley TMD (specifying it was for 150s). Seems like Tyseley will have nothing to do with the MV operation this time round.
I think the drivers were all in one link, mixed traction they call it, it has a bit of everything in it, but thats the only link where the 230's were, those drivers worked 319's too as well as 350's and I believe it is them who are also being trained up on 730s. There were six diagrams if I remember rightly, one or two had a mix of mainline and Marston but the others were purely Bedford work.
All new depot staff for Bletchley, the 230 project was maintained by VivaRail fitters, all of whom got made redundant at the back end of last year. Tyseley will still be used for heavy maintenance in the event of a major failure, Bletchley for the day to day stuff, exams and fuelling. Suppose they will have to get replacement parts in, tools and everything else which goes with that.