fish only tend the school/shoal when under stress or feeling at threat, their normal behaviour is to stay in a loose group generally together but not in a tight swimming group, with a 45 gallon tank you could have roughly 45 inches of medium sized fish, add up the adult size of the fish you have now then you will see how many inches you have left.
i dont know whether you could get a another group of fish, bleeding heart tetras should be kept as a group, a lot of sites with fish advice arent all that great, id only keep them in a group keeping them in a pair isnt really fair.
your stocking sounds good at the moment, its always best to understock than overstock, bear in mind your bristlenose plecos will get quite a bit bigger, (between 4 and 8 inches depends on the species) your RTBS should be fully grown by now aswell so it shouldnt effect the stocking anymore.