Bluegill, first of all, you need to decide just how important flyfishing is to you. I got into the guiding game about 6 years ago, and after about three seasons I had some experiences that nearly took the enjoyment out of the sport for me. At that point I decided to step back a bit and diversify. I went from doing 90 plus trips a season to doing 30 or so, and was alot happier.
Guiding is a lot of work. Everyone that wants to be a guide, I think realizes this somewhat, though they never truly appreciate it until it's too late.
Leonard is right about a couple of things. First, it is pretty expensive. If you guide throgh a shop, in all likelyhood they'll provide rods, waders and such to the sports. Everything else is usually up to you. To give you some idea: I just went over my tackle receipts for this past season. Heres the breakdown; 32 full day trips, after tips figure an average of 350 to 400 a day before expenses. mileage $3700 and change, flies, tippet, lines, leaders, indicators, split shot and so on $2650 (at a 30% shop discount or pro deal pricing) Lunches, drinks $1200 (aprox.)
You do the math. Thats more like a hobby than a living as far as I'm concerned, and thats considering that I didn't have to pay for the outfitter liscense, insurance or river permits.
One more bit of advice. You needn't be a casting instructor; you're only guiding most folks for a day or two at the most and that's not enough time to even begin to get them to the point where they can get a dryfly where it needs to be. The thing to do is figure out ways to get the client onto fish without having to cast well ie nymphing. Get good at nymphing and your sucess as a guide will increase greatly.