I think most has been covered. Change/add to your circulation. MTS to help keep the sand bed from getting anaerobic. Do the worked needed to keep it clean. I have a tank that uses very lightly colored play sand and it can be a chore, but I like the overall look.
Apart from that, your tank sounds awesome. Have any pictures to share?
Wall 1, the Driftwood over there isn't going to be much help with creating flow.
Brand of PH/CP isn't going to be too important, but I'd likely go with Koralia or VorTech depending on budget. Size will likely depend in how much your sand might end up moving, I would likely stay well under 1000GPH, but really depends on your use, getting something DC might be best so you can turn it down if needed and get something bigger than you think you want.
Circulation pump, direct current.Sorry about the silly clarification .. I know PH stands for Power Head ... what does CP stand for? and what is DC?