My EBJD is the calmest fish in my tank. He messes with no-one unless they mess with him (in which they don't). I have successfully raised him 5 months now and he is 3 inches. With their genetics, I don't know if he will be getting any larger but he really loves seaweed, bloodworms, and red wriggler worms. ( I raise my own) I don't even put the seaweed in there for him but he goes to town with it. As far as plecos, I only keep ones that will grow from 4-6 inches. I have a rio negro pleco and a flash pleco. Both beautiful and will stay small.
I initially bought 3 EBJD at 1/2 inch but two of them died early on, I never replaced them because I just wanted to follow through with him. He has always been my favorite so I guess I may have willed him into growing. I think maybe another factor is I only kept him with other babies and there was really no aggression. I kept my water changes up and water quality and far as softness and pH and they had ALOT of space.
Now with them all between 2.5-3.5 inches, they all still have a lot of space and territory.
I only have 7 fish (all of which are SA/CA cichlids), 3 plecos, and four cory cats in my 125g tank. 6 of the fish will not get over 6-8 inches and neither will the plecos.
This is all to give you an idea. I think you should just buy 3 just to see if they will flourish and go from there. As far as tank mates or school fish, pick some options and gradually dwindle them down so you can see your preference as far as looks, personalities, and hardiness. Make your water quality to fit the EBJD.