Just have to pick up my 75g tank!

Hey guys. It's me again. I've finally got everything I need either here or on the way for my 75 mg build. Got my two heaters, return pump, skimmer, lights, Ro/di unit, salinity tester, now I just need my tank. I have 2 tanks I'm combining into one. A 10 gallon with 2 occ. clowns and a 30 gallon with a fire clown, blue damsel, and six line wrasse. Should I add the 2 clowns first, since they are smaller than all the other fish or should I do all at once, or what. I don't really want to loose any fish but I know sometimes things happen. I just want to avoid it. A 75 should be big enough for 2 clown families. Well 1.5