Cichlids are fun! You dont have to use sand from the pet store. I bought a HUGE bag of pool filter sand from my local garden center and chunks of slate rocks broken off their huge slate garden rocks all for under $20! Or you can just use regular gravel. I still keep plants in my cichlid tank and they dont up-root them as much as some people say. If you do cichlids, Malawi species are a good start.
Platys and mollies or swordtails are an upgrade from the guppies.
I had oscars in my 55 gallon at one point and they required so many water changes. I found them to be dirtier then goldfish, but that was just my experience some people might have a different opinion.
I did a tetra and small fish set-up once. I loaded it with a bunch of different kinds of tetras.

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