I would skip the ammonia and nitrite test kits. Because if you can already detect nitrate (no3) it means the bacteria are already present and already at work .
To play it safe wait another week and slowly SLOWLY stock your tank.
I have a big rock (bout size open hand ) that has the following 7 coral .
1) GSP
2) Unknown zoa
3) Green paly(green people eater)
4) a couple of Gold cloves (started with many heads but my sixline ate them)
5) red maxi anemone
6) green monti
7) pink Birdnest Sps
Selling @ $38
Hydrometer are easiest to use , if u can't use it , then u r gonna have even more problem using the refractometer. Get your tank volume correct and do the maths. Every packet or bucket of salt comes with direction to use ..