6 Firemouths are the best answer in a 36x18 tank. 6 will insure a pair. Then remove the other 4. Not because they will be killed but because your tank is to short. Cichlids are substrate spawners that defend territories in the wild 4'x'4 square. That's 16 sq. feet!!! Your tank is 4.5 sq. feet. I like 180g and up for cichlids to do their best. Smaller tanks will work but until you but them in a 6'x2'x2' plus tank will you really say WOW to cichlids.
As far as the plec goes...The firemouths will attack the plec so get one that is cheap and expendable.
If you can sex the fish Then I would selectively breed the best colors together to get fish like this...

As far as the plec goes...The firemouths will attack the plec so get one that is cheap and expendable.
If you can sex the fish Then I would selectively breed the best colors together to get fish like this...


