Not sure if you have gotten an answer elsewhere but i will answer to the best of my ability anyways lol.
Firstly, they are stunning little things..... if you are dedicating to breeding then i would go species only, some like to add a few small dithers but tbh ive never found that necessary, although cory's can be a nice addition and keep a little movement in the tank... just be aware though, 260's like the water on the warm side so a cory suited to higher temps is the best option...sterbai are a superb option.
In all honesty, your tank is a little big for a dedicated breeder, only because it has the effect of the plecs possibly staying within there specified 'territorial zone', however that doesn't mean they wont breed..... a good ratio for plecs is 1 male to 2-3 females but with that sized tank and plenty of caves and hidey holes, you 'could' get away with 2-3 males and then females to suit.
Your tank by measurements is coming up at around 340l?..... ive had groups of 10+ in 180l tanks so it gives you a sort of idea on potential group sizes.... but a group of 10-12 sounds a nice number with your sized tank.
