Build it by all means but take it easy and keep common sense in mind. More than half of us don't feel comfortable going over 25/30 mph on a bike , forget a damn scooter.
I offer you an alternative braking Solution. (y);) Here's a guy that is actually using your recommended braking method in his pickup truck Rocket...lol...Thought you might get a kick out of this...lol. https://www.youtube.com/watch?v=J8LCh3ZE3p8
Just know your limitations and ride within them, you'll get good at it. Yes you can just push off, I thought you were still in the planning stage and hadn't bought the motor yet.
Looks exciting in a kamikaze sort of way. I've seen battery powered ones just booking it at least 20mph. They have bigger tires and wheels. Full on motocross gear would help with the tumble but not if you hit something solid like a brick wall or a freight truck. Lol.