In the interests of keeping things light and simple, I'd consider a Fuji 645 zoom. I'd prefer 6x6, and it's obviously nice to have the flexability of a full system style camera but compromised have to be made - they're dirt cheap too. The Fuji will fit in your coat pocket, and do most of what a full system would.

You could alternativly just take your Rollei - stick with the 75mm standard lens in MF, and use the 35mm to give you more flexability.