When turned into Lords, your companions should each start with 200 renown, and from then on it should be treated like the renown of other NPC Nobles.
As far as their stats and leveling goes, I'm honestly not sure.
Each companion, once granted the land and title, will start with an army of around 40 men or so. Most of them will begin with soldiers of whatever culture/faction corresponds to their land, but there are some exceptions (or at least, there was in beta, I'm not 100% sure if that's still true). For instance, when given a previously Swadian castle/village, Bunduk spawned with a Rhodok army (which matches his culture).
As for further recruitment, I think they'll end up recruiting whatever troop types your villages can produce. AI Lords can also generate troops without actually engaging in village recruitment, and I assume your companions will as well. I'm not exactly sure how that functions, but I think they get soldiers based on the castle that they garrison during that time.