Wow... quite a bit going on here.
Just to jump in the middle... you are getting some great advice. Take your time completing the water changes, the speed that you do them isn't as important as the fact that you are completing them. If it takes two hours to refill the tank, that's fine.
One note about the water changes and the salt... when you are replacing the water, you need to replace the salt as well.
So, if you added 4 grams of salt for the full tank here's some quick math for you:
A 20% water change means you've removed 0.8 grams of salt with that water and need to replace the 0.8 grams. Add the salt to the water before adding it back to the tank, and make sure the salt is completely dissolved before adding it.
A 30% change means 1.2 grams of salt.
40% change means 1.6 grams of salt.
50% change means 2 grams of salt.
60% change means 2.4 grams
70% change means 2.8 grams
80% change means 3.2 grams.