I'm told there are some Mahindra tractors with greater than 25hp that run clean enough to eschew dpf. I don't know which models, but it might be worth looking into.
It sounds to me that you could definitely use a tractor. 25hp is probably big enough unless you need to lift really heavy stuff, say 1500 to 2000 lbs or more on a regular basis. One thing you need to consider is maneuverability. You said you have a park like property. I assume you have lots...