if you don't mind all the noise, you could post signs around your town advertising go-kart racing for a small fee it would help maintain the go-karts and you would even be able to close it down on the weekends or something when you need some "quiet time"

also, i'm not sure but i think i saw go-karts at like wal-mart or something.... the type of go-karts really depends on the course you're making.... if you have more of a stadium course (e.g. nascar or something) you may feel safer with the faster kart, but if you're making a fun, windey course, the slow ones will probably be safer