Lasius niger is a monogynous species.
But the species can found their colony by pleometrosis. However after the first workers have hatched they will kill all queens except for one (there is also a risk that even the remaining queen will be damaged). I think there is no limit in the number of queens. Someone tried it out with 20 queens as far as I remember with no problems.
It doesn't really matter if you build a vertical or horizontal nest, if you build a vertical one make the chambers deeper and if you build a horizontal one make them wider.
Edited by Barristan, June 25 2015 - 10:47 AM.