Well, the gouramis vary greatly in temperment and size. Some species can be very aggressive and some very passive. On the other hand some speices may peak growth at 2" and others may get massive. It would help to look into the growth/aggression tendencies for each type that you happen to take a liking to.
There are very many varieties like golds, blues, opalines, pinks, pearls, powder blue, fire, honey, red dwarf, sparkling, paradise, chocolate, samurai, giant, and snakeskin...to name a few.....
Many are passive, but some of the more readily seen "pet shop" varieties like the golds, blues, and opalines, can be somewhat aggressive and not like having competition with other "like" gouramis in the tank. Some are and some aren't. All of these get slightly bigger, but tend to stay within 4-5 inches at full growth
The dwarfs, chocolate, honey, and fire...which are sometimes seen tend to be passive and stay smaller.
The pinks, giants, paradise, can get a bit bigger.
Putting too many different types together can lead to aggressive competition, but with these fish, each has a different personality. I would stay away from the blues, opalines, and golds if you are going to have may different types in a tank. These guys grow pretty quickly and usually like to chase the others, casuing stress and nipped fins.
Some breeds like the chocolate are for experienced aquarists that have a certain water quality. They are a liitle more difficult to take care of. Just do a little research before you buy and decide what is best. If it looks like they arent getting along...separate them, because this probably won't change, and you will end up with a dead/dying fish soon.