Motorcross bike what should i do?

hi im just wondering a few things first of all i want to get a motorcross bike, i just turned 19 and im short im only 5 foot 3 1/2 i was looking at crf150rb the big wheels but i dunno if that is to small for me the seat height is only 32 inches i only rode pw80s and a ton of quads rangeing from blasters to yzf450s so i want to know if its hard ot be shorter and ride a cr125 or a crf250 i want ot start racing but i want ot be able ot control the bike ? Also is it possible to lower the crf250 down like a few inches its a few inches higher than the crf150 and i wouldent be able to reach? let me know thanks!