The number of a type of Unit you can take is limited by it's
AVA (availability). So example I can take 2 Intruders in a basic Nomad list but I can take 4 Securitate. You can take as many as you have availability of anything available to your faction.
So if for example you though the new Hexa Sniper looked badarse...
You may want to consider PanOceania,
If you play around with the army builder you can get a feel for the different forces and options...
http://infinitythegame.com/dt_army/ (requires adobe air)
And here is the gallery of all the miniatures...
http://www.infinitythegame.com/infinity/en/facciones/
Also, feel free to swing by the official forums and the guys there can answer anything and everything about whatever faction you may think of.