I think most forks use a spring system and plastic guides for alignment. In many cases the springs wear loosing tension and the plastic guides wear and allow the fork to wobble, vibrate and have poor control. Most of the springs can be adjusted to increase tension so you could look for an adjustment bolt. This will offset some of the wear in the spring and will acomidate a heavier rider. IF you know someone with a lathe they can make new plastic guide pistons for you to re-tighten the fork. I believe there are true shock forks usng hydraulics but that would be at the uper end of bikes. And I've never heard of and using straight pneumatic.

About the only thing you can do for a 500w front hub is install a good torque arm and pray. But if you want a rear chain drive why do you think you also need a front hub as a back up? IF you really feel you need a backup setup then install twin chain motors. I did one with twin chain driven motors that were totally independent other the the final chain.

Bob