I disagree on most of your points. These fish may be okay in an adequately sized tank compatibility wise, but all of them in a 75 is a problem waiting to happen IMO. Theyll likely be fine for a while, but i dont see these fish working out bioload wise as full grown adults.
I do agree on not adding tankmates. Another potential issue is if the Jd happen to pair up.
And no, aquarium salt isn't helping anything and shouldn't be used as a supplement or preventative. Salt is a good treatment for certain ailments but wait for them to arise, otherwise you are just playing chemist every water change.
I also have noticed that most of the people that dose aquarium salt don't even have a refractometer or hydrometer to monitor their levels.