Okay, I believe I have finalized my level-up details. Going with the third setup for a decent AC for the eidolon.
[sblock=Barrik Level 4]
Summoner 4
+1 Ability Score (Charisma)
+X HP (yet to roll). +1 for Favored Class
+1 BAB (total 3), +1 Will Save (total 4).
+1 Handle Animal, +1 Knowledge (Planes), +1 Knowledge (religion), +1 Ride, +1 Use Magic Device.
Learn 2 2nd-level spells, gain 1 2nd-level spell slot/day (plus bonus spells). (Bull’s Strength, Lesser Evolution Surge)
Gain Shield Ally class feature.
Gain 2 Evolution Points. Drop Reach to recover 1 Evolution Point. Take Head and Bite evolutions.
Evolutions (spent points): 2 extra head, 1 extra bite, 2 trip, 1 fire resist, 1 Imp Nat Armor has the better AC.
[/sblock]
I'm going to wait on an OK to update Barrik and Gulujak.