Guppy,
I would suggest for your first time that you use a handler. He can give you the ins and out of the paperwork. Sometimes the few dollars you pay them is well worth the cost.
That said. You will definately need Mexican Insurance. And permits. However, most of the tourist airports, like Cabo, Cancun, Cozemel, etc don't cause problems with private flights about permits. The smaller airports will. The major tourist airports know that they will kill the golden goose. Also the Tourism Boards keep on them about it.
I have found that as long as your going in there to spend money, they don't cause too many problems.
Next payments. Cabo will take credit cards for fuel and fees. However many Mexican airports will not. Cash is still king in Mexico, especially USD. Don't forget to tip just aobut everyone. The fuelers, the commandate, the airways people. $10 is normal, $20 for extra service. If you are going to be a regular, once in a while tip a little extra. I have found that dounuts (Krispy Creme) go over good. On a hot day a soda or two for the fuelers goes over good.
Be aware that Cabo's normal operating hours are short. About six they go into overtime. It can be expensive. If you are going to be a regular down there, make some contacts there, it will make the trip easier.
Have fun.