One gourami shouldn't be a problem. Are you going with a honey? Keeping male and female guppies will lead to many, many guppies. Keep that in mind. And just to clarify about school sizes: the bigger the better. While you can keep 6 of a schooling fish together, it is not going to be as effective as 12 or 24 [although generally odd numbers are thought to be more pleasing than even]. The more fish, the better the school will look and the more confident they will be. But it is true that less active fish will be affected by more boisterous fish. The corydoras should add plenty of activity to the bottom of the tank and the rasboras to the top. Let us know what you decide in the end and put up a picture once it's done.
really hope just have 1 gourami doesn't stress him/her out because of being lonely
