i'm dont know much about compatibility with guppies but i've had bad experiences with my gourami...i own a opaline gourami, which im pretty sure is the same thing as a blue gourami maybe just a color variation? My opaline was orginally in a 20g a while back with a bunch of other fish....it ended up trying to eat my cardinals and killing my dalmation molly, which was about an half inch bigger than it! so i moved it to the 30g with cherry barbs, next day i find cherry barbs with missing tails... i rearranged all of the decor and made tons of "natural" barriers. Since all of the other fish stick to basically the lower left area of the tank to avoid him....I moved my cardinals to the 30 and now for some reason he's not bothereing them.... I'd never put my gourami with a german blue ram, but idk it might vary from gourami to gourami, best thing to do is to just get whatever gourami you want to and if it doesn't work then return it asap..make sure to get females though, and thats another thing, mines a single female! im probably going to try and get rid of her in a couple weeks...