Some possibly useful info on resources at the party's disposal:
Mattias' followers (with level-up adjustments):
Priests: 10x Adp1, 10 x Ari1, 10x Exp1, 1x Adp2, 1x Exp2, 1x Ari3, 1x Adp4, 1x Adp6
Temple Guards: 15x War 1, 2x War2, 1x War3, 1x War 4
Temple Staff/Servants: 10x Com1, 5x Exp1, 1x Com2, 1x Exp2, 1x Com3, 1x Exp 5
Phillip's followers:
Heavy Infantry: 26x War1, 2x War2, 1x War 5
Heavy Cavalry: 6x Ari1, 1x Ari3, 1x Ari6
Archers: 8x War1, 2x War2, 1x War3
Scouts/Skirmishers: 5x War1, 1x Exp1/War1, 1x Exp2/War2
Support Staff: 10x Com1, 3x Exp1, 2x Apd1, 1x Com2, 1x Adp3, 1x Exp4
Potter's Creek Militia:
10x Adp1, 2x Adp2, 1x Adp3
40x Com1, 25x Com2, 12x Com3, 6x Com4, 3x Com5, 1x Com6
4x Exp1, 16x Exp2, 8x Exp 3, 4x Exp4, 2x Exp5, 1x Exp6
17x War1, 6x War2, 3x War3, 1x War4
1x Ftr2, 3x Ftr1
Led by Magh Ironthews (Ftr5/Exp1)
Potter's Creek Druid Circle (includes normally independent hunters/trappers and wanderers who will follow Darla):
5x Adp1, 1x Apd2
4x Exp2/War1, 2x Exp3/War1
4x Drd1, 2x Drd2
2x Rgr1, 1x Rgr2
Led by Darla (Drd6)
Other Notables:
Old Man Caldor (Hedge Mage) Wiz3
Effie (Wise Woman) Com10
Elizar Burne (Mayor) Ari3
Garath (Sheriff) War5
Father Garlon (Priest) Clr4
Helt (Town Drunk - other than Max)
?
Juutar Bachin (Merchant) Exp8
Kessa (Innkeeper) Brd4
Meridee (healer/mid-wife) Adp4
Yslar Quilcia (trader) Rog5
"The Young Heroes"
Christian Caldor Ftr2
Sister Gwenta Clr2
Magnus Wiz2
Timoth the Tailor Rog2
Given enough time, you could probably scrounge up enough folk to triple the size of the militia from surrounding smaller communities and independent farmsteads, but they would not have any experience or training operating together as a unit.
You also have the following allies/contacts:
The Phoenix Court (helpful, and Captain Felosial has offered aid, but made it clear she will not sacrifice forces in a fruitless battle, and the Court has been weakened after bearing the brunt of assaults by the forces of the Magus and then the Storm King, and they need to hold forces in reserve to protect the forest).
Druids of the Thornwood (fairly powerful, but extremely unlikely to intervene).
Lizardfolk of the Saltmarsh (Aramil, wherever he is, had excellent relations with them, and some of you did hunt down one of their renegades and slay the Black Dragon of the Marsh, but lizardfolk rarely venture in any numbers out of their marsh).
Karak Ungor (you have excellent relations with the Frostsilver Clan, and at least contact with the Dwarf King's representative, but dwarves are notorious for closing their gates and holing up in their karaks when danger approaches).
Aes Garathon (Leo is a member of a prominent noble house - but a young member with little or no influence with his family. You have decent contacts with House Arcturus - at least with the matriarch, but bad relations with the heir apparent, Sir Xander, who would be the one leading their forces into battle. And you have no actual contacts with any of the other noble houses, any of the guilds, or any of the prominent churches except the Church of Ithwe).
Bob the Hermit (the guy who told you about Athanor's blade, Giantkiller, and seemed to know more than he let on about Olot, the Orb of Night, and the Thornwood).
The Orb of Night (via Olot's demands, you know that there is a powerful artifact in a ruin of the Dawn Empire deep in the Thornwood - though you don't know what it does, what dangers guard it, or how the Druids of the Thornwood would react to an intrusion to gain it).
The Library of Telos (you know more or less how to get there, and Mattias and Galen have already passed their entry tests - maybe there is some knowledge there that can help you?)
Other Adventurers (Max in particular had contact with members of several other adventuring parties who had been at the Library researching how to stop the Storm King - but no way in particular to contact them).
The Third Empire (you know that there is a powerful, resurgent human empire in the lands of the Old Empire - but it is far away, seems pretty xenophobic towards non-humans, particularly elves, and you don't actually have any contacts with the Empire itself).
The Bone Hills (you know that many fallen heroes of the Atlantean Empire - and their kewl lewt - are buried in the Hills; the blade Giantslayer was pivotal in defeating Olot. Of course, desecrating Athanor's grave apparently roused large numbers of undead, and there's a Justicar patrolling the Hills who doesn't like you very much and is likely to oppose any effort to loot more tombs - not to mention the Vampire Lord, Valen, that has come after you a few times).
The Magus (you know that there is a wizardly warlord in the Wilderlands to the east, who apparently has found the fabled Atlantean Foundry, and is using it to assemble an army of warforged and other constructs. But is he a potential ally against the orc horde, or a still greater threat?)