Like Leslie, he's a "blank slate" and can be turned into anything the player needs/wants him to be given enough time, from a tough foot solider on par to Frederick, an archer almost able to match Diev, or a heavy cavalier able to match any of the more combat suited companions. He joins the company with only a set of nobleman's attire, woolen hose and a knife, so it is recommended to have at least a cheap sword/spear and a shield for him to work with when you take him on. You also can simply keep him as a medic if you want.
He will hire on with you for free.
He is a noble, making him lord will result on him recruiting Empire troops.
Making Ansen a lord is a good idea, as he has an Upstanding personality and you can have the ability to gear him out from level 1 however you like. It will take some doing - and likely some potions from Finneas de Digit - to make him a truly effective warrior, but once you have your own kingdom having a loyal lord with a full war party is more important than if that former companion actually is effective in combat. From level, get him just enough strength (perhaps 12-13) to wear some decent gear, and then go whole hog into upping his INT, CHA, leadership and trainer skills, and also putting some points into pathfinding. He starts with an above-average wound treatment skill; upping that might not be a bad idea.
He dislikes having Boadice gather support for your claim on the Pendorian Throne.