You should post on the mechanics board. My understanding is you have to match your rear hub to the cassette you choose. Your bike probably shipped with a 7 speed shimano mega range cassette. I would stick with that.
As to chain line. I chucked the crankset that came with my CX and bought a road Shimano 105 square crankset on eBay and used only the 42t chaing ring with a 122mm UN-73 BB. The Chainline hits gear 4 dead on.
2000 Montague CX, I do not recommend it, but still ride it.
Strida 3, I recommend it for rides < 10mi wo steep hills.
2006 Rowbike 720 Sport, I recommend it as an exercise bike.
1996 Birdy, Recommend.
Wieleder CARiBIKE (folding), decent frame.