Aquarium salt won't do anything against ich/ick until the concentration is too high for the freshwater fish to handle.
Heat treatment requires high 80s. Slowly turn the heat up to at least 86F and let it stay there for at least a week. Most strains of ick won't be able to reproduce at such temperature, and once they complete their life cycle they will fall off the fish and die.
It is a good idea to use a quarantine tank for new fish. Wait for at least two weeks to see if there is any sign of disease and parasites before move them to your established tank. It can avoid spread the disease and parasites to your old fish.
To use Tetra SafeStart, just dump the whole bottle into the tank at once. Do not do "doses". Once the bottle is opened, the bacteria spores in there will become useless pretty soon. You need to use the whole bottle immediately after opened it. There is also no point doing "doses" from the point view of getting your tank established. Once the tank is established, it is established and no longer need any more "doses". All it needs is one big dose to get it to establish as soon as possible. In case you still have any Tetra SafeStart left in your unsealed bottle, I suggest you use it all in your tank immediately. If it is the same bottle you have used since weeks ago, I'd think it is already quite useless by now.
As for water changes, it will not affect the bacteria as long as the filter media stays in the water all the time. These bacteria are waterborne, and they must stay wet to survive.
