I would not put killies in with mudskippers...they are surprisingly aggressive and adaptable...they will live, but probably not the mudskipper. I'd set up the tank in the basement anyway, and only add those animals that will take the heat. Killies will do fine...just keep them at a minimum, and realize that males will lose breeding color, if they have them. Mud snails will do fine, and you can add them by the fistful. Shrimp will last awhile....hermits for a few weeks at most. Little mud crabs will do well, but they turn into big mudcrabs, (granted, that's still small, but they have strong claws...they are related to stone crabs)which will make the tank uninhabitable for anything in reach. Bank mussels (Geukensia demissus) will also do well for awhile, but only add 1 or 2, otherwise they'll starve. I used to keep a local tank during the summer, with only a corner filter, changing the water with saltmarsh creek water, then releasing everything at the end of the summer. I still keep a local 10 gal. tank in the city...with hermits...temp does drop into the low 60's in winter though. You may also want to consider setting the tank up now with all the invertebrates, but getting sailfin mollies instead of killies.