Alienist requires the ability to cast at least one level 3 summoning spell, and Knowledge (the Planes), 8 ranks. I'd want to keep a familiar (given nifty familiar boosts), and take all 10 levels of Alienist.
Knowledge Devotion is an option to get 8 ranks of Knowledge by level 5. What else?
(Another option would be a wizard, maybe a Focused Specialist. Isn't there a feat that gives wizards spontaneous casting for summoning spells?)