I agree with
@fermentedhiker , the old guideline of 1 lb per rock per gallon is outdated. Besides, rock weight is probably a horrible measure of a rocks contribution to filtration and biodiversity. Lighter, more porous rock is better than denser, heavier rock in my experience.
You have plenty of rock. Create the aquascape you want for visual appeal and functionality, even if you wind up removing a lot of the rock. If you plan on using sand, you will have a huge area that bacteria can grow on. If you are really concerned about bacteria populations, get some ceramic media like a marine pure block or some balls and throw in your sump. Those will house significantly more bacteria than your rockwork.
Now I may be totally wrong in the below view and I hope others will correct me if it is incorrect, but I have held the view that our bacteria populations are largely dependent on the bio load that is present in a tank and surface area. For instance, a tank with 2 fish producing ammonia are going to support less bacteria than a tank with 6 fish for instance. Bacteria typically will multiply and populate as ample food sources allow. Certainly there is an upper limit to this process, and you also don't want to add too many fish at once, as your bacteria have to adjust to the increased ammonia production (not to mention other nutrient issues from overstocking). Your system will create a balanced eco system over time given your bio load. There is usually plenty of surface area for bacteria to grow on inside the tank, so I usually concern myself more with proper stocking levels for the tank size and nutrient export methods available than the amount of live rock I use.