My BB got really aggressive once she decided to start spawning, otherwise wasnt too bad. Probably wouldnt want to mix her with other viejas just in case.
The aggression is all based on the individual fish. If your going to rule out Zonatus and BB because of aggression than you better rule out all Fens also, because they are the most tenacious and aggressive in my tank.
I started out in my grow out tank(135gal) when all of these were around 2", 4 x Zonatus, 4x B/R hd Fen, 4 x Catamaco, 4 x Hartwegi, 4 x Argentea, and 4 x Syn. When they doubled in size, give or take, I picked one of each and put them in a 240gal. In another grow out tank I raised, starting at the same size, 4 x Zonatus, 4 x Bifasciatus, 4x BB, 4 x Piebold Fen, 4 x Breidohri, 4 x Regani. The Breidohri are still in the 135 grow out. They (at least in my experience) grow extremely slow.
In the 240 they joined 3 x Delhezi Poly, 2 x Nicaraguensis, and 2 x Sieboldi. Ya, the tank had a lot of fish in it, but at 4-5" it didnt look crowded at all. They were able to survive in the 240 with the occasional pulling of certain fish. (not do to aggression but because they were either growing to slow (Breidohri) or were just out grown by the others. I had several spawns in the tank, and no serious damage was done.
Because I think that a Vieja/Paratheraps (or whatever they call them now) tank is a beautiful tank. Now they are in a 300 gal. Here is the stock. 12" male Bifa, 10" female BB, 10" male Catamaco, 7" female Catamaco, 9" male B/R head Fen, 7" female Piebold Fen, 10" Argentea, 10" female Regani, 8" male Regani, 7" female Regani, 6" Syn, 3 x Delhezi Poly (all 10"+), male and female Bocourti 6". And 4 exotic plecos, gold nugget, king tiger, vampire, royal. All living and doing well. In fact I just pulled a few hundred of the Catamaco fry that just started swimming Monday.
Your probably wondering where are the Zonatus and the Hartwegi. Well, I had some requests for their fry, and it was much easier on me to remove them and put them in their own tank. Since I have thousands of their fry now, lol, I have recently stuck the Zo's in my other 300 with my Hoga pair, 12" Heterospila, Pearsi, Bocourti, Godmanni, Robertsoni. Just a nice mix of goodness. The Hartwegi went into my 400gal breeding tank with a pair of Argentea, Trimacs, Ecuadorian Festae, and Lyonsi.
The moral of this long drawn out story is. Dont rule out a fish that you really like just because of what you read. Every fish is different and all of them can be nasty as all get out. I have several stories of non aggressive fish just opening a can on more aggressive larger fish. Yes, the fish do get more aggressive when they spawn, but it has not been to bad. (knock on wood) You will have your ups and downs.
In my opinion and what has worked really well for me is starting the fish young and living in a community, let them grow together. Whenever I transfer a fish from one tank to another, I have very little aggression amongst the tank mates. Call me lucky, I suppose, but it has been very successful so far. The only time that I have issues, is when I introduce a new fish of adult size, then its usually the new fish that is not use to the community and has to flex on the others.
If your able to expand in a year to a larger tank, then get what you want at a small size, watch and enjoy them grow. Watch their personalities from a young age, when they get large enough to move to another tank you will by then know which ones have the perfect personality for that next stage. I think that you will enjoy this the most.
If your not able to expand in the future, then I would still grab 4 of what you like at a young age and size, and watch them grow. Dont rule out anything, cause any fish can be an a**, and any fish can be perfect.