LPG can be stored indefinitely; and can be used for both -LPG cooking stove and LPG generator (LPG generators are modified gas generators).
Hope that helps a little...
Gas is easier to obtain and has more uses. Unless you convert all your equipment to diesel, you'll always need some gas around your property.
As for the storage, I had gasoline stored for 5 years with no issues. If you have two tanks, you can rotate it and use it in your cars.
Just the other day, I was driving my diesel truck in a new city and could not find a gas station that would sell diesel. I had this truck for 3 years and this is the second time I had this issue. Never again diesel trucks or cars for me. Every gas station sells gasoline.
As for diesel generators, you would need one with an electric heater (that would run from a battery) to warm it up in -10C or below temperatures. Around 0C it should start ok as are your tractors.