Mexican Street Dog

Hey, I'm looking to get my first BMX bike and I'm wondering how to get one that fits.

I'm 6'2" and 170lbs. The difference in top tube length is so small, from 20" to 21", it seems weird to me that it can make that much difference. I'm guessing I need one on the longer end. Do I need to get the longest? Or will a 20.5 work?

Also, how about handlebar height? There are so many variations, stem up or down, and the size of the handlebar itself.

Thanks for answering a noobs questions, sorry if these are already answered somewhere else, i couldn't find them.