Hi welcome to the forum

Hard water can be a bit limiting but it depends on what you want, for a big fish community you could look at a mix of some Central American Cichlids like Rainbows, Sajica, Nicaraguans, Cutteri or Firemouths, Live bearers like Mollies or Swordtails, Golden Panchax, Rainbowfish like Bosemani or Millenium (any of the larger species) and Synodontis Catfish. For a small fish community you could look at Rummy Nose Rasboras, Emerald Rasboras, Galaxy Rasboras, Thick Lipped Gourami (red or regular), Rosy Loaches, Inle Loaches, Espei Rasboras and Croaking Gourami.
Or you could really embrace your hard water and go for a Rift Lake Cichlid tank either from Lake Malawi or Tanganyika. Malawi offers the best colours, Tanganyika offers interesting behaviour (but still some stunning species). In a 4x2x2 like you have either a Malawi Mbuna or male Peacock and Hap tank would work great but both take a few extra levels of planning but big rewards.
Wills