Dean, I have a 10 acre place with 8 horses. I also have a 1957 861 with a front end loader. I use my tractor for light bush hogging, scrapping snow and hauling round bales out. We do not have a manure spreader, besides our horses live outside.
I have been very pleased with my tractor, it was in less than great shape (understatement) when I bought it. Between the helpful folks on this site and a couple of instructional videos, I have been able to get all of my work done. Getting parts has not been a problem. Overall I would rate the (well OK, my) 861 as a reliable machine. Enough power for every task that I have put it to, although I did have to get used to bush hogging the taller grass a little slower than the MF255D that I used to have. If you have a front end loader, get get power steering.
Cannot comment on the 3600/2600.