I would go to HiFiEngine and download the user\maintenance manual. Sign up if you don't have an account-it's free and they don't spam.
I bet a lot of your questions will be answered. In good operating condition, they are very good decks, if you need 8 channels and can stomach the price of tape. Being aimed at the pro market, it may well have seen considerable use, so head condition needs to be considered. Relapping of the heads can cost you as much as a solid consumer level 1/4" quarter track machine, and such a machine will allow recording a stereo source on each direction of tape.
Tascam was Teac's pro line of R2R's