Please note the following NEVERs

NEVER put an unwound back on a wound body (Or visa versa) - always always make sure they're in sync
NEVER change the shutter speed after you've mirror lockup'ed
NEVER do anything less than a full turn both ways. If your back isn't moving smoothly, it needs a service. Continue to try and fiddle with it and you'll end up with your back still needing a service and your camera needing some unlocking.

Be careful with her and she'll treat you well. I love mine and wouldn't swap it for anything in the world. (I do augment however with a mamiya 6)

My understanding is the Rollei and Zeiss made lenses are both of equally high standard. The coating on the HFT lenses is better than the non-HFT so in difficult light, sure there is a difference. But its a medium format camera and you will want to be using a hood anyway.
Don't have any direct experience re the 120mm vs 150mm. The 120mm is apparently very sharp (but note that its f5.6, so some of that might be depth of field related, and some will be eroded by the fact its harder to focus). The 150mm is a bit softer and suits portraits better.

A decent strap is worthwhile getting. Hoods are a must IMHO