Just a couple of thoughts:
A betta has the same threat display as a gourami, so not a good combo, and a betta will terrorize/eat your shrimp. Would a 2 gallon all in one tank be an option?
Re: killifish--as a past member of the AKA, and a current member of the Greater Cinci Killifish Assn, I can tell you that Fundulopanchax spp (Fp. gardneriw, striatum, walkeri, etc) are not good combos with bettas--they have the same threat displays, and the killifish are far more maneuverable, resulting in shredded bettas. Diapteron spp are generally more delicate and not good beginner fish (fundulopanchax spp are far more hardy). BIV/BIT complex (Aphyosemion bivittatum and bitaeniatum) are relatively small shy fish which will be bullied by the betta (gorgeous in a well planted 10 g species tank, though).
If you want more info about killies, drop me a PM and I'll be glad to help!