There are several ways you can build a pet based class and it will depend on what type of damage you want your pets to be doing. Have a look in the build compendium for those classes and see what others have used.
As an example, here’s JayNyne’s Conjurer build which started out as a poison based mostly one, but later as further updates were made to the game, became a lightning based one.
Go to grimtools calc and then to the devotion tree. Then use the search function and search for “to all pets” and look which ones gives defensive bonues like resistances, health, armor, defensive ability to start with.