I believe a companion's initial starting level will depend on that of the player character's own when they first meet. So, they will not be optimized for anything in particular. That said, it is hard to make a mistake in this game if you have a general idea of what you are doing and provided that you are not on Path of the Damned difficulty with Trial of Iron on. Micro Details, such as character attributes and talents, are important and optimization is king here. But, Macro Details such as party composition, strategies and resource management are easier to change on the fly and are more concerned with generally winning as opposed to "overkill."
So, you just need to decide which companions are going to tank, dps or play support and try to allocate stats from there (at least that is how I perceive it). Granted, you will want to compose a sizeable portion of your party (counting yourself) of actual optimized characters to ensure a steady progress through the game - basically walk into Gilded Vale and drop 500 cp for 2 brand new characters then you will have 3 slots available for companions of your choice so you can get all the banter you want. I cannot stress that the first thing you should do after getting out of the tutorial zone is to buy new companions you might need.