First, deal with your tensioner issue. The stock tensioner mount is a decent piece of equipment and, if locked down properly, should be able to fight the forces placed on it by the chain. Wrench it up tight and use some blue threadlocker for insurance. You don't have to use the stock plastic roller. I grind down a thick steel clevis to fit the mount and use thick nylon washers as the chain surface, sandwiching them between two stainless 2" fender washers. There's no one way to do this.
I have had good results with $35 steel wheels from my local bicycle shop. Just be sure to properly adjust the bearings and check for true before building up your rag joint. As the wheel is subject to incredible pressures of motorizing, there is going to be some distortion over time. I used to use wider tires, but quite by accident I found that a thick rubber 1.75" tire works very well. It actually stiffens the rear wheel and provides a better, smoother ride and the slimmer fit eliminates any chain slap from the drive chain. Consider the steel wheel to have a one year lifespan and you should be fine.