I like to fully prep a bike before I ride it. I hate losing fasteners.
What size are the wheels? That will determine if the bike is large enough for you. I changed Son of Weldangrind's wheels from 14/12 to 17/14, and that lasted until he hit six feet. After that, he needed a full size frame.
I wouldn't make any changes to the bikes, unless they don't meet your needs. My Son's 125 was too fast out of the box, so I re-geared it to be much steeper. It cut down the top speed, and allowed him to climb anything he pointed it at.
I hope you enjoy your new bikes.
