I have 6 green sunfish in with a Tiger Oscar, and surprisingly their hasn't been a problem. They school together and even mingle with the Oscar. All were wild caught and have adapted to captive living very well. They regularly eat pond pellets and fresh seafood chunks. I actually got rid of my African cichlids in favor of good old North American natives. The oscar was just adopted from a friend and has adapted well to his new American friends.
How many you keep in a 55 will depend on their aggression level. They can be aggressive like cichlids, so sometimes they don't tolerate other green sunfish. In a much larger tank you could do a large group of them and it would spread the aggression, but a 55g is really too small for that, so you'll have to stick with either 1, or 2 so they can make their own territories.
As far as how often they spawn in a tank, it's really not that hard, but you can't keep the female with the male in a 55g because he's going to ferociously guard the nest from her after they spawn and he might kill her.
Raise the temperature to about 80. Wait until the male builds a nest and the female develops eggs and lays them in the nest. Remove female. The male will guard the nest and the eggs until they hatch. Once he's done guarding the nest you'll have to remove the fry because he'll eat them.
And on another note, here was my beautiful green sunfish male (i know sex because he built a nest):
And an even more attractive sunfish species, which I would highly recommend if you can find any, the longear:
wel im thinking of buying a bigger tank
but we have to buy the sunfish here
and its mainly all pumpkinseed so me and tom where verry lucky to find some greens
the store where my bro got one says its to late in the season to get more
so i went looking for them all over the country
finaly found 3 more
so i hope its a couple otherwise i will have to wait a year to get more of them!
i think longears are imposseble to find in my country
the only sunfish they sell might just be the green and the pumpkinseed!
