I would say go with 8-10 dwarf corys or 6 "bigger" corys...but instead of killies (meh) try a group of 6-10 smaller colorful tetras or rasboras. You want an easy to take care of tank for your first try. We want you & you fish be happy & healthy. Then maybe you will want to move on to other fish, as many of us have...but you need success early on to want to continue in our hobby...& we do want that for you...& pics too, lol.