You've built a nice looking bike. Simple and clean and the install looks sound.
Here's a link to a center stand that I've had very good luck with.
Electric Bike Accessory - Heavy duty kickstand A bit pricy but holds the weight of a Motorized Bicycle just fine. Have you tried some heat on that rusted bolt? It looks like an aluminum mount? The steel bolt might loosen if you apply a little heat to the mount. Ride careful, have fun.
Tom