Best way to keep it clean is by never running it. But what's the fun in that?

Cleaning depends on what your running it on/in. Personally I avoid running in mud of any sort and even skip wet rainy days. For the most part I like to have cans of computer duster handy. Just be careful as its very possible to force grit into bearings and other sensitive area's with compressed air. From there, I just take things apart and clean as needed.

As far as the Trophy Flux is concerned its sort of limited on what's available for 'mods'. I wouldn't spend too much on it if it were mine. If running(bashing) off road only, I'd spring for Proline Badlands. But that's just me and the surface I bash on. So again, depends on how your using the rig and what surfaces you run on. Probably not a bad idea to start looking into steering servo upgrades. Stock HPI ones don't last too long.

Other than that, I'd just replace things as you break them. My reasoning for not getting too spendy is from my own experiences with the Trophy series. They are a okay vehicle...sort of a starter vehicle to get you feet wet, but at least here in the US they don't get much support from HPI as far as option or aluminum goodies go. The aftermarket don't offer much either.