Depends on the gourami for pretty much all questions. But generally almost all gouramis sold are males. The females tend to be dull in colour and are generally a special order.
Different gouramis have different levels of aggression, though it should be noted that all gouramis have the potential for aggressive behaviour.
Also different gouramis get to be different sizes. Some stay 2-3 inches in size, others get to be over 1 foot long. So tank type is a very important thing.
Gouramis like planted aquariums or at least places to hide. More hiding places will mean less aggression.
Finally, never keep them with fish that are nippy, especially fish like tiger barbs. They will probably get their feelers nipped off and will go through a lot of stress.