Most of them are very peaceful and 3-4 inches. Apistogramma borelli is neat. Apistogramma brevis. Apistograma pertensis. Apistogramma viejita. Apistogramma gibbiceps. Apistogramma guttatta. Thats just a few. They are not commonly sold at LFS but fairly easy to get online from places like Aquabid and from private sellers.
Peresonally I wouldn't put the gourami with the apistos but thats just me. Wouldn't get a male, might be aggression between the apistos and gourami. Not sure...
When breeding them they need very good water parameters and a place to spawn. From what I have heard from people getting them to spawn is not hard but raising the fry is and the less chance for predation(other fish in the tank-hence my inclination to not add the gourami) the greater chance the fry will survive.
So I would suggest a pair of apistos and some cory's or some other bottom dweller that will fit in your tank. Possibly an ancistrus sp. 3?
There are over 400 types of plecos. Not all get 25 inches as platy ben said. He is more than likely referring to a common pleco. Most ancistrus(bristlenose) species stay between 4 and 6 inches. There are other plecos that stay under 7 inches: L333, L18, L107, L144. I could go on forever.
www.planetcatfish.com is a good resource for plecosand all other catfish(corydora, otocinclus, synodontis, etc)