it sounds like you really have a passion for this motocross thing!
Honda CRF 250r no question for you.
Its got a smaller engine for the lighter weight, beginner riders. the power is fun, NOT scary like the 450 for a beginner. Honda makes a very reliable bike which rarely ever break. The suspension on a Motocross racing bike such as the 250 is designed for the bumps and jumps of the Motocross track, instead of a off-road trail bike that weigh a ton!