I SW is harder to maintain cuase you have to make sure the parameter doesn't change becuase the fish are not so forgiving and yeah is very expensive.
You do need a hydrometer/refractometer its like you life line. If you don't know what the SG is then you don't know if your add too much or too little salt into the tank. It takes me about a day to get it right. I set up my water about two days before the water change it due.
The smaller the worse. You parameters will change fast if given the time. For example if a fish dies in a 20 the toxics will have less room to spread so it'll get to the other side faster than with a 55.
If your doing a FOWLR your greatest expense will porably be LR. But its worth it. LR will help you with so many things.
