You are doing the most profitable part of a kite business already, selling your time, which costs you nothing. The problem with being a dealer, you first have to buy the stock, then hope you can sell it. So, given you are teaching and effectively creating your customer base, you do have an edge in that you can mentor your clients into the products you wish to carry, providing you operate in a territory un cluttered by other accounts.
I'm assuming you're in the states, so likely you'll have some room about you, so it will be about generating your client base, you should also consider something else like SUP or Wake if you have a cable nearby to supplement those periods when the wind lets you down. Also in the future, de seasonalise the business with snow products, but again be careful not to load yourself up with crap you can't sell.
Margins, generally they suck, until you have the turnover and volume with which to negotiate better deals you'll be looking at best at a 50% mark up, thirty to thirty three percent gros. There are brands who offer more, but generally they are the weak brands that don't sell, so they try to shoe their kit in with tempting 40 - 41% margins but you soon find them all over the net with 20 to 30% off.
The net is your biggest enemy, tossers coming in trying your kit and asking for you to price match some lame deal on this or that site, trying on wetsuits then disappearing, so a good exercise is for you to ask about see what 'deals' you can get on the brands in your territory then steer clear of them.
Try and buy close out end of season stuff, don't engage in 'percent' deals, quote discounts in cash, saying 'Dude I'll give you 100 bucks off, sounds better than saying I'll give you ten per cent for example. Buy kit to chuck in with a deal, its a sad fact that kite and windsurfers are wise asses that always want a deal, they'll wander into walmart or apple store and pay the going rate but they'll try and shaft the very hands that are trying to exist off servicing their every needs every time, in short better do something else, but if you must, you need to become what you yanks refer to as a bit of a 'wise guy'.