I will start with buying a new battery and blowing up the tires. In my younger days, I bought a 1928 Buick Standard with 10,000 miles on the odometer that had sat since 1941 in a garage. I poured some gasoline into the fuel pump, put a battery into it, and stepped on the starter. The engine came to life and ran for about 3 or 4 minutes when it died and wouldn't start again. Most of the valve springs had broken from being in compression for all those years. New valve springs, and it ran perfectly again.
In your case, you might want to change the oil and filters, before trying to start it. If you are really lucky, there will be no mouse nests to chewed wires to deal with. Check everywhere for evidence those critters never inhabited your tractor. Remove all traces of them before you do anything. If you are so inclined, give it a good bath and also spray any moving parts on the engine to make sure that they are not stuck. Unlike a gasoline engine, once the diesel starts, if the stop solenoid isn't working, it will be difficult to shut it down. If it has a manual transmission, be certain that it is in neutral before starting.