I'm sort of the same:
1) 900' long driveway so I have a front-end snowblower.
2) mowing with a mid- mount mower
3) miscellaneous FEL, BH, and pallet fork use
I figured a generic 2000 hours on the engine for costing things out using it 100 hours/ year. 20 years at 100 hours per? A good estimate...