rotax makes their own exhaust and it is specifically designed for their engines. you will get more power out of that than any of the aftermarket companies
i don't think so. not from what i've seen. ask your local BRP dealership. i know you can get them i just don't know where from check parts unlimited or a parts catalouge
ron wood is the rotax master....we have one with his exhaust. wow!! make sure you get the baffle kit if you plane on riding it somewhere noise is a factor.....LOUD http://www.rotax.net/