No. There is nothing wrong with rasbora, provided they are one (or more) species of the smaller sized rasboras, and these are fine with the group of cories. One of the "dwarf" cory species (Corydoras pygmaeus, C. habrosus) would work best, but a group of one of the medium-sized species is also OK.
But when it comes to gourami, rams and betta, there are significant problems. A male Betta is not a community fish and should not even be considered here. As for gourami, yes, there are some small-sized species. The sparkling pygmy gourami (Trichopsis pumila) in a group of five would be nice, and have no issues with rasboras and cories or other peaceful fish like some of the small and less-active tetras. There are some other small gourami species rarely seen too.
As for rams...the common or blue ram in any of its varieties (they are all derived from the same natural species Mikrogeophagus ramirezi) needs warmth, at least 80F but preferably higher, and this will burn out the cories and is not very good for the rasboras or small tetras either. The Bolivian Ram (M. altispinosus) does not need such warmth, and a single fish can work and given the tank's length (a 20g long is 30 inches/75 cm) this is OK.
Your water is very soft, so all of these are good on that front. There are still upper level fish like hatchetfish and some of the pencilfish to go with these. Obviously not all of them, but the options are vast.