If your goal is to get it running as cheaply as possible, then yes, you should try to get it running first.
If, on the other hand, your goal is to learn as much as you can, do the job as well as you can, and have as much fun as it's legal to have, then a complete teardown is the way to go. The problem is, this can get seriously expensive. I spent over $4000 doing mine, most of it on engine work. I tore down everything except the transmission (trannies scare me, and it worked, so...) cleaned, inspected, repaired and painted everything, and put it back together. Took me just over a year in my spare time, and I'd do it again in a second.
I should mention that mine was in terrible shape, and I had to replace the block (used, $75) the head (NOS, $450) magneto (professionally rebuilt, $225), manifold (new reproduction, $220) and sleeves/pistons/rings (new, $300)
The F12 is a very simple tractor, and an excellent choice for the first-time restorer. Parts are readily available and compared to some tractors (can you say John Deere?) inexpensive.