Piston:
Roughly how many stumps can you grind in a day? I'm starting to think that a tractor with a grapple and a 3-point stump grinder may be the best "DIY" option for my situation.
Wow, well unclebuck, that really is a hard question for me to answer. It would depend on many things, obviously size of stump being one major factor. You mentioned most of yours are 12"-14" diameter. Also, how high are they? If they are close to the ground, 3" or so, you can get them down really fast. If they're 2' off the ground, you'd be better off cutting them down with a chainsaw, and then grinding them.
Is it really rocky where you are?
If the stumps are pretty close together, and less than 14" in diameter, and lets say 3" above ground level, then I could grind a stump like that in 5-10min.
I mostly grind larger stumps which take me somewhere between 10-20min a piece, but we're talking about 24"+ diamter, that flare out a lot right at the surface, so I would have to reposition multiple times. With a 14" stump, I'd probably start near the back of the stump, move forward 8" or so, and do the front of the stump, if you wanted to get down deep. If you just wanted it 6" below the surface, you could get away with not moving at all. I think the stumpgrinder has a 3' diameter wheel on it, so it can take a good size stump.
Look through some of my old posts on stumpgrinding. I have done a lot less stumps than some people on here. Check out some posts by Foggy and I THINK mossflowerwoods, or mosswoods???
ALso keep in mind, that my stumpgrinder is rated at 35-100pto hp. I have 39, so I'm at the bottom end of power. If I were you, I would look at 50hp+ and you would demolish those stumps in no time.
For a dream setup, check out Pclausen's thread on his stumpgrinder.
Type the following into a google search and you'll come up with some good estimates of your own.
Shaver SC50 stumpgrinder site:
www.tractorbynet.comm
Shaver SC25 stumpgrinder site:
www.tractorbynet.comm
Woods SG50 stumpgrinder site:
www.tractorbynet.comm
Woods SG100 stumpgrinder site:
www.tractorbynet.comm
(only use one "m" I had to put 2 in or it hyperlinked funny)
also, if you type those into google (just copy and past them) then search google images, you'll come up with some great pictures.
I have been trying to think of a better setup than a good sized tractor, FEL grapple, and PTO stumpgrinder, for your situation (minimal ground disturbance for erosion, and creating something along the lines of pasture land) and I honestly can't think of anything better, assuming you want to do it yourself with equipment you want to own.
There are much faster (and costlier, and less fun) ways to do this, but I think a setup such as this would be a very good way to go, in my opinion. (just get more power than I have!)