I don't see any problems in your plan. The more live rock, the better you are off. If you added another 25 to 40 lbs. to the 50 you plan to have, you could remove your bio balls and have a more natural filtration system. This is the whole idea to the deep sand bed as well.
I don't see why you are running a live sand bed however. You do not have a reef tank, and you will not really be able to keep too many sand-sifting critters to keep your substrate clean because of your triggers, and you will not be able to disturb it too often or too much to clean it because that will harm the sand bed more than it will help it. I think you would probably be better off going with a 1" aragonite substrate, an oversized protein skimmer to remove wastes, a few powerheads for good water circulation, and a wet/dry to remove particles and to move water. However, you know your triggers. If you can keep snails, stars, and hermit crabs with no problems, then the sand bed is a great idea for natural filtration. I am all about the natural way, but in your case, it sounds like it would be more detrimental than helpful.
Also, I really don't see you maxing yourself out with those 3 fish. With the filtration system I described above, only feeding every few days, and regular water changes, you should be able to keep one more good sized fish in the tank with no problems.
