If you've got the income, you should probably buy a minimal setup that you could use 95% of the time. For most people, that's a pack and two heads. Depending on your local rental houses, I'd go with brands that you can easily rent additional equipment for. Profoto, Elinchrom, Speedotron, and Dynalite are usually available in most rental shops, but you should check. Quantum flashes are also handy and not too expensive. If you have business insurance, most rental houses will let you rent for the cost of your deductible, if you provide them with your insurance information. That might be the smartest way to go.