The filter floss will almost instantly cycle the tank.
A small handful of platies and four or five guppies in a 20g tank would be pretty easy to care for. More than that could be done, but you'd have to do more water changes.
That last seems to be pushing it for a 27g, especially with the gourami, which can be very territorial in smaller tanks. One gourami, a half a dozen barbs (give or take, depending on the kind), and the pleco (only while it stays small) would probably do well.
This is all, of course, just my opinion.
