For a BW/SW setup you need to use a marine salt mix. Most likely the salt you are talking about is sodium chloride which will not make a BW/SW setup. Marine salt has lots of other trace elements in it.
As for fish you could house some GSPs and/or ceylons. Both do well in a high BW/SW setup. I know you could do 2 but I would probably not add 3. I keep my GSP in an 80 himself and it doesn't look empty
With you wanting to go eventually to marine like Penpitt said I think Green Spotted puffers or Ceylons would be ideal for you, especially if you got them young and then as they grow you will get closer and closer to a marine setup.
My Puffers: Puffers I have kept: T lineatus T miurus A modestus T biocellatus C valentini C coranata C papuan C lorteti DPs suvattii burrfish T niphobles
nikitanain wrote: (scats, monos, gobies) small to medium sized fish would be great
LOL, scats grow the size of a dinner plate & most monos growe to a foot long! There are not really a lot of colorful BW fish, although their personalities are quite "colorful"! The prettiest-colored BW fish IMO, is the figure 8 puffer. If you want a nice community, you could keep several of them, along with different species of gobies & then you wouldn't have to go higher than a SG of 1.005. If you are looking to keep SW fish eventually, then go with the above suggestion of GSPs & or Ceylon puffer. Then, once it reaches marine, you could add a tomato clownfish or a school of damselfish.
You are getting sleepy... you only hear the sound of my voice... you must do water changes... water changes... water changes... water changes...