I would get two, but my breeding tank is already in use with gold fish/coi and maybe tench, once there out the way i can think about more breeding.
As it is i have 2 males and 6 females in my tank, i hope they wont breed lol i dont want to have to kill their eggs or live babys.
Edit: if i were to get one fish, would it be very agressive if i added another a week or two etc after?
1 Pleco, then 3weeks later add another of the same breed, but oposite sex.