Motocross start which machine?

Tach together, after a long search I came across this forum and would like to ask some questions here, hope that one or other nice guy can give me after a long time it is finally where I can finally feel the desire to buy a Motocross machine, now which one? 125s, 250s or yet 450s I tend rather to a suzi rmz450, but is that also the right thing for me?? I am 35, do not want to operate the whole extremely, is anyway too late already for the k ich mal , that so still could become something out of me but just to turn on weekends in sand pit or in forest few round, which results later from the whole is still open. The thing should have power because I am also a little overweight should also pull me up the mountain What would you advise me in this case? The machine will be a good used up to approx. 3000€ and exactly before that I am afraid when the things were extremely agitated that I buy cat in bag and fas I don’t want to fall on my nose. Then I have one more question, the parts are not allowed to stress, you still have to have them insured in such a gravel pit can not happen much you think, but what if something happens… Then to the clothing: helmet, boots, shirt and pants is clear but I really need this jacket with protectors