The plants may or may not have issues with the meds. Bacopa is picky. I would say if you only have 2 in there, don't buy any more plants until after the treatment. Treatment will only last less than a week. Then, do your water change, put carbon back into the filter, and wait 48 - 72 hrs more before adding new plants. By then it should be safe.
If you wish to save the plants you have now, I would suggest removing them from the tank during treatment. So long as they stay wet and get light, a few days out of the tank and they should be just fine. I'm not one for uprooting plants, but in this instance, because of the fish in the tank, the choices for meds is quite specific.
As for the salt issue... 4 tbsp in a 55 gallon is not going to have any medicinal value to your fish. I'm with Blue on that issue, I'd stop the salt. Gouramis can be sensitive to heavy levels of salt, and for a 55 gallon tank used as medicine, you would need about 1 cup of salt, and marine salt... not standard aquarium salt. Your safest bet is to use one of the meds I named, and skip the salt. Your small dose of aquarium salt will likely cause more harm than good over time, especially for the dwarf gouramis.
Hope this helps. If you need anything else, let me know.