Rodent damage to a unit's electrical or electronic engine/transmission controls, that has not been used much, can quickly add up to thousands in repairs. Don't sign on the dotted line until you can do a complete inspection of the inside and the UNDERSIDE looking for any signs of rodent infestation/damage. 
Belts that have sat for years should be replaced. The rubber tends to harden in the position it was kept. Considering the hassle when a belt breaks, it is cheap common sense to replace them at your convenience than to have to deal with a broken belt on the side of the road. 
Flush the brake system completely, which will use 3-4 QUARTS of fluid and have the calipers inspected to insure that the slides are not frozen. The Calipers and pad should be OK. The discs may have surface rust but check for any pitting. 
The generator may need a complete service, and an inspection for insect damage. 
This could be a good deal if everything checks out, especially if you can do a lot of the work.