Hi
No-one else seems to be answering so I will try.
How do you plan to spread gravel? With a bucket on a front loader or by pushing bit with a blade on the back of the tractor? If you are using a front loader you may want a slightly bigger tractor so that it is more stable when you have a heavy bucket of gravel on the front.
Most old tractors are fundimentally pretty reliable due to their simplicity. I have a 1958 Fordson that has done all the work on the croft for the last 3 years, you have to be willing to basic jobs like changing leaking oil seals though.
Old tractors might not have power steering and their hydraulics might be a bit basic for running a post hole borer.
My 30hp tractor runs a 4ft flail mower no problem over most ground but the engine has to work really hard when mowing thick rushes. I don't think I would want less than 30hp for my situation.
I am not familiar with the John Deere range or with the used market in the US (apologies if I am wrong in assuming you are in the US) but JD do have a good reputation.