It doesn't matter how big or how small your tank is, there's always somebody else with a comparative "monster".
I've only had these fish for a bit over a year, so I'm far from expert on their quirks. If it were me, I would buy a group of babies, raise them up until you can sex them, and then keep the best male and 3 females. It seems that the male will breed with multiple ladies, rather than pairing up with one and then beating up all the others as some cichlids would do. I wouldn't put two males into that tank, because they are still cichlids and that sounds like a fight, or at least an unhealthy intimidation, waiting to happen.
And if it were mine, I wouldn't put in other fish, simply because I like sparsely populated tanks. You could certainly get away with a few cool-tolerant Corydoras like C.paleatus, but the balzani are typical sand-sifting eartheaters and other bottom-feeders aren't going to be needed unless you want them. I have a few Scleromystax (formerly Corydoras) barbatus in my tank, just because I like them.
And again, I'm sure you could swing a few carefully chosen tetras as well; both choices you mentioned would probably be good in those temps. I wouldn't do it just because I like buying schooling fish like that in at least a group of 10 or so, and then we're back to that crowded tank thing of mine. If you keep up with water changes I'm sure its doable, just not pleasing to my eye. If some small fish are a must-have, I'd go with the Bloodfins because the BA tetras get fairly large.
Personally, I'd prefer some kind of livebearers in that tank. I love the look of big fish and little fish together, and tiny livebearer fry growing up amongst relatively large fish like balzani looks good to me.