I need cichlid and other freshwater fish help!?

[S H]

I have a 35 gallon aquarium and was wondering what kind of fish I can have....I have 4 goldfish for the winter..i have the tetra whisper filter....what do i need for cichlids (air pumps,heater, etc.) and what size for each...I am also interested in any other kinds of fish.....what different species of fish get along....my goldfish will be gone in the springtime....oh, by the way, I have nothing in my tank tank ecxcept for fish so is sand or gravel better and what kinds of decorations do fish like.....Thank you so much for helping a novice fish wrangler!