Yes it's 1/4". I'm pretty sure the R8 can only record on 4 tracks at one time, but I might be wrong. Maybe they did two different models, like with the A-8 which have a "Live Recording" version that can record on all tracks at one time.
I assume that you are in the process of byuing one? I have an A-8LR, which is an excellent machine. The R8 is basically a newer version of the A-8 and is most likely quite excellent too. Things to check before buying is tape-wear. If the head is worn its no disaster, but you can't realign the tape head without relapping the head, so thats a risk for an extra cost. So if there is tape wear, you must check that the head is properly aligned before buying it. (I was lucky. I didn't check, but the tape is properly aligned.. Phew! ).