First thought I would have is BUY a used race bike, don't set up your own race bike and turn a street bike into a race bike. The reason is costs. I've looked into it because apparently I have too much time on my hands, and conservative estimates to convert a Ninja 250 into a race bike range from $1000-2000 easily (unpainted bodywork alone is going to cost you a few hundred, for example).

To do a 600 or an SV650 it would cost more because you must use a steering damper in most cases, most bikes are going to require case guards that a 250 isn't going to require, etc. Plus once you get into it, then you're going to be tempted to upgrade suspension components, at least at the backend, which can cost some money.

Finally, if you set up a race bike, you've got to safety wire it. If you've never done it, it's not trivial. Not to say it's impossible, but it's something you must take care of to race with the MRA and might not be something you can or want to deal with. Putting a drill to your 1098's bolts is likely going to cause you some discomfort.

Just my opinion, but take advantage of what someone else is selling before trying to convert a street bike into a race bike. I'll let others chime in before I say anything about WHAT to race (250, 600, SV, etc.).

Cheers,
Jamie