Set a budget. Your extra electrical use can be calculated from each heater or lamp you use. Figure out the food costs, supplies and a vet fund. The maintenance costs of each animal you add leaves less money for the rest of them, and you.
Pay as you go.
NO CREDIT!
As someone else stated above, Life Happens: Natural disasters, car wrecks, apendicitis, cancer, blown disks, babies, deaths in the family, lay-offs, hyper inflation, deflation, violent crime, etc.
Don't take on more than you can handle.
It won't be fun.