I'm not finding any stat blocks for Servo-Skulls. In Dark Heresy 1E, I simply considered them another character that went on the PC's turn (they could move, aid, attack, get attacked, etc. as normal). How do they function in DH2E? Are they basically pieces of equipment that hover close to the character and give him whatever mechanical bonuses are listed under their entry (and that's it)? Perhaps I was overestimating their ability in 1E, but I considered them more capable and open to more options than that.

As written, DH2E considers them simply items. There are different kinds of servo skulls such as vox casters or tech assistant ones, which generally dictates what you can do. Lore-wise there are more advance uses as you describe but so far 2E hasn't covered that ground yet.

Your options are to either just throw up some stats yourself or if you have access to Black Crusade's core rulebook they have a whole system for making minion characters. A servo-skull is one of the character examples and looking there would be a great start.

My group has made stats for servo-skulls, partially because we've used or encountered armed ones, and have one of our own. Gunner, the Bolt Pistol servo-skull with a German WWI-style carapace helmet, also has a small speaker built in to blare Flight of the Valkyies. The Tech-Priest wouldn't name him Wagner...