I have a good bit of experience with this, and can offer some practical advice.
While I was in grad school I was usually running 2 games at a time.
The regular game for the for classmates, and and the "community outreach" game which included visiting high school students and soldiers from the base.
As the games were held as part of a recognized university club at least some of our functions had to have an "open door" policy to qualify to use university facilities...Sometimes I had 4 players...sometimes I had 15, +cohorts, pets, ect...with player ability levels ranging from "can I try" to "it was different in the blue book days..."
I've also have been playing Kingmaker...
So, advice for your specific situation first:
1) Find a copy of The Wizards Amulet/The Crucible of Freya/supplemental material (necromancer Games). Also, The Burning Plague (free wotc) and Hobgoblin outpost (MMIII or II web enhancement). Pick a corner of your Kingmaker map and plunk the Crucible area into it. It is a isolated struggling village that faces constant raids from orcs/goblins.....
The civilization bringing heros ( your pcs) can bounce back and forth between the 2 areas putting out fires, and keeping up with the xp ramp....
Also, look for Crown of the Kobold king (piazo) and The thieves in the Forrest.( I forget, Penumbra?) Isolated lumber camp with a problem and isolated river fishing outpost with a bandit problem....Remember the lumber camp / drynad problem and bandit problems in King maker? Relate them.
In short, just make the low level section of the adventure path longer.
2) See if you can find some 1e modules to run/integrate into the adventure path. They are built on the assumption of a 7-10 member party and are usually not too difficult to convert on the fly. Watch out about higher modules though, as the 3e versions of the monsters are often much tougher.
3) Sometimes during mass combat I would have problems with everybody clumping up on initiative. The solution was to x5 the init mods and roll on a D100.
4) If combat ends up scattered across a large area or multiple levels of a castle, i would use zone initiative. Say divide the map into quarters or sixths, or sides of the river, floor of the castle....Pcs and monsters types roll initiative with in their zone. then go around the map clock wise or up from the basement, running events in each zone in turn. If someone crosses a zone boundary they start at the end of the que for that zone when its turn starts.
5) other times i would use a "what you see is what you get" system with the minis. If i have orks, you are fighting orks. use either critter type initiative for the monsters, or "Now it's a monster's turn" with each round "that" monster is the one closest to the PCs , each in turn until the mosters are less numerous than the pcs.
6)
if you happen to have a magnetic white board....
use magnets. a pair of each magnet. One for location, the other for the initiative list. also get a yardstick, forget the grid, and just use the ruler for spell area and movement distance.
7)
No, you may not have a petal dragonfire adept cohort with the entangling breath feat, much less 2 of them. do youself a favor and just ban metabreath feats for pcs unless you like reworking effective ability scores for monsters every round in mass combat!
anyway...