its very simple
take MSF
buy a used bike (its your first bike, not your last)
start on a ninja 250, sv650, ninja 650r, or one of the other many 650 twin bikes that are available and work your way up.

most of the folks you will see that say o i started on a 600 or a liter bike bought it to A. look cool and B. to ride like an idiot down the freeway. You can have fun on any bike if you are riding it properly.

best of luck to ya