A couple of things . . .
They are probably the closest thing to Clan sibkos you will find outside the Dragoons in as someone mentioned, they take in children (how do they find them?) to train as warriors and like the Clans culturally program the children. In this case, instead of the programming saying the Clan is the greatest, they are taught their House's philosophy and service to the Confederation/Chancellor . . . which one is supreme depends on interpretation of the House philosophy, Lorix Order and how much is the Chancellor the Confederation. Like the Clans they will have problems replacing their losses unless they take in older candidates- which we saw how that turned out with the Capellan Solution.
The military organization typically has a mech battalion and then one or more conventional battalions. Strength & composition depends on the House philosophy, the more militant House the more numerous their troops.
New Warrior Houses can be formed, but I am not sure of the timeline they were introduced . . . Warrior House Ijori was reformed in the opening stages of the Dark Ages (see By Temptations & By War) but between the Jihad and the Dark Ages a new Warrior House was founded by the CapCon.