a lot of hobbyists go by the rule of 1 pound of rock for every 1 gallon of water, but you don't need to do that. i have seen many tanks with more rock and tanks with less rock. the reason for live rock is for your biological filtration, because the bacteria that converts dangerous ammonia to the much more harmless nitrate lives on there. this rule was established because it is a fairly even balance between the stock of the tank and how much bacteria is actually eating the ammonia. some rock is more dense, and some rock is less dense. it really comes down to surface area in the end.
for circulation, you need a fair amount of water flow to agitate the water so gas exchange can occur. gas exchange is how fish get their oxygen. i would go with a tunze 6105, because they are controllable and are basically bulletproof. i made a thread asking what the best pump was, and someone had a full inch of coralline algae on their tunze 6105. those pumps an take abuse. even better would be 2, because you do want to put circulation through you rockwork to avoid any detritus buildup.
for a return pump, i would go with an Eheim 1260 or 1262. many people have had success with them.
for a 75 gallon tank, i would get a skimmer. if you plan to stock heavily, the skimmer will definitely help export some of the nutrients from all the fish. it is usually always recommended to get a skimmer on a tank.
i would not put any tangs in a 75 gallon tank, because many tangs get to 6"-7" or more, and yes, this includes bristletooth tangs. it is just not right to put a 7 inch fish in a tiny 75 gallon tank. fish that you could put in are dwarf angels, basslets, blennies, cardinals, clownfish, damsels, firefish, dottybacks, maybe a pygmy filefish, gobies, and wrasses.
i hope this helped!