1. Your readings seem to be perfect. A little too perfect, but yeah... perfect. I know it's expensive, but you should definitely add more rock. 1 - 1 1/2 pounds per gallon is normally recommended. What are you using to test the salinity? If it's a hydrometer, you should compare it with the reading of a refractometer. Hydrometers are notoriously inaccurate. I started off with an IO hydrometer. It read 1.023 SG, when in actuality it was 1.031 SG. Most refractometers compensate for temperature, and are the best way to get accurate measurements.
2. Clowns are not very aggressive, so it might be better to pass on that if you are going for triggers and groupers. If it can get the clown in it's mouth, it will eat it. You also mentioned these in plural. I think you should check to see how big the fish you listed will grow to be, and the space requirements for them. 75 gallons will run out of room in a hurry when you start adding large fish. The largest fish in my 125 might reach 7". Bigger fish require bigger and better filtration as they can create quite a large amount of waste. Bigger mouths equal bigger poop.
