The Yashicamats are great, I shot with one for months before getting my Hasselblad. I still shoot it on occasion, as it is lighter and has a decent built-in reflective meter. I'd highly suggest one as an affordable alternative to the Rollei.
If you do get a TLR, make sure the front plate that the lenses are mounted on is flat. When I was getting my Mat, I had a friend tell me how important this was, as he had bought one that had been dropped and the front plate was uneven. If the plate is uneven you end up with a different focus between the groundglass and the film plane, and that's no good. Also make sure that the linkage between the shutter/apo and meter is intact, I had to repair mine to get the meter to work right.
As mentioned above, MF really changes the way you take photographs. Not only are you looking at subjects with a different perspective (be it waistlevel or even through a prism), you only have 12 exposures per roll. You'll end up focusing on making every shot count, and start focusing on composition and the like with a better eye. I loved when I changed from 35mm, but I still shoot it when I need a faster system.
Bonchance!