I suggest avoiding using an owlbear in the mite/kobold part of the path as an encounter with a particular owlbear is quite important later and you don't want to go to that same well too often.
I think "Pog" in the monster builder is just a named goblin. He should work ok. A couple other options I found in the builder, if you go for an artillery type monster instead of a controller:
- advanced gnome entropist (they are level 8 to start, so tack a couple levels and elite it, maybe using a template of some kind.)
- Three-Tooth (no idea the source but appears to be a level 10 elite kobold artillery)
- Gurn Sirensong (again no idea the original source, but he's a level 9 elite gnome artillery with wizard-y powers like magic missile)
There is a "task" in there called Tuskgutter, which involves the PCs finding a wild boar that has been causing havoc. I can always substitute an owlbear there instead...