Some of the best advice I can offer is to read this:
http://festivalprose.com/so-you-want-to-work-at-a-renaissance-festival-part-two.html It's written by a Tortuga, and he knows what he's talking about.
No one else can help you decide on your act, because ultimately you have to do something that you will not mind doing over and over and over and over (and over...) again, while at the same time constantly working to improve.
Or, in your opinion, what are the more desirable roles that could ensure a spot at just about every renaissance faire in the nation?
There is no such act. What works for one faire will not work for another, depending on location, audience demographics, and what the owners and entertainment directors want. What I would suggest is that you check out what acts exist on the circuit, and then find a niche that isn't being filled, or at least isn't being filled in the faires you're interested in. Fairies, for instance, are pretty much covered. Mermaids are very popular right now, but the initial expense of tails and tanks is HUGE. Jugglers, stilt-walkers, acrobats, magicians, etc all exist, but there may be room for more depending on the festival in question.
The street is a tricky, difficult place to make a living. I will be frank with you: you will never make as much as the stage acts. There is also a ceiling to the amount you can reasonably expect to make in tips (with some exceptions, especially for wildly popular fairies who are tireless marketing geniuses), and it is a lower ceiling than stage performers. Figuring out how to get tips without destroying your act is also tricky, though in my experience it is easier to get tips as a musician than it is as the sort of act your chef would be. The more instruments you play (well) the more marketable you'll be, but ultimately you want to make sure your act is engaging regardless of the instrument.
My biggest piece of advice is to figure out an act, and then to take that act to your local faire(s) to learn how to present it in a lower-stakes environment. If you can, camp during this time and make sure you know exactly what you're getting into wrt: the living situation on the circuit. Again, check out the link above. It has excellent information.