Help....Salt to Fresh

I just got a great deal on a 75 gal. with stand two great filters everything. I used to be very into the hobby with a 55 gal. tank with community live breeding fish mollys guppies etc. My question is the person I purchased this from didn't clean it at all it was caked with inches of salt and I worked for hours and hours cleaning. Do you think I could convert it to fresh water? Secondly any suggestions on fish? I had Oscars but the live food and my son is 5 so I'm not sure I want to get him into that just yet. Like the hobby and want something very nice looking with fish that are hardy enough for me to get back into the hobby without costing my a fourtune. Any suggestions and help would be greatly appreciated.
The other thing is I have 20 gallon my stepson has and he is interested so I'm going to use that for guppies ect.
Thanks

if you clean out the salt you should be good. african cichlids are always a good choice and pretty easy to keep.

I was thinking about cichlids they look good but are aggressive....correct? Could you give me a quick run down on what I might be able to mix with them and what type of substrate. I'll do some research because they look colorful and from what I understand there are a lot of varieties. Can you add a pleco or some type of a big bottom fish with them maybe some kind of catfish

There are tons of routes to go with cichlids. Most of them are not as aggressive as people believe, just make a list of what you like and research and post on here what your thinking and we can help you out. I have catfish and plecos in all my tanks with no problems, even have a tank with cory catfish and Africans. Pool filter sand is a great substrate and is cheap. You can get it at home depot for $5 one bag easily does a 55g