The fact of having a large force wouldn't be a problem. Where he would get the numbers for such a force is. The Sorcerous Kingdom has somewhere close to a million citizens; divided up across multiple races. Now Ainz could arm and deploy every man woman and child, but that would seriously undermine the grand and glorious image he wants the SK to have.
But if you just want numbers fine.
999,500 Untrained human peasant/farmers/smiths/children and all manner of people not suited for combat
500 trained human town guards, adventurers, clerics, mages the strongest being Mithril ranked adventures
10,000 Quagoa
18 White Dragons
80-200 Frost Giants(estimate)
800 Untrained Lizardmen
300 Trained Lizardmen
10,000 Orcs and Zorn
and 5,000 Goblins the strongest being level 43
Now the numbers of Nazarick. Note: Many, many, of those mentioned here have the ability to summon and create even more allies; They will get an * near there name.
*11,000 pop undead(6,000 stronger than Mythril Adventures)
*500 (conservative minimum) to 4,000 (Almost impossible maximum) Mid-tier Undead(Each as strong an Adamantine Adventurer or stronger)
Kyouhukou's cockroach army (numbers unknown)
*Shalltear's vampire brides (numbers unknown)(level unknown)
*Shalltear's undead vassals (numbers unknown)(level 80 or so)
Cocytus's Guardian Knights (numbers unknown)(level unknown)
Cocytus's Lord Knights (numbers unknown)(level 70)
Cocytus's 6 Frost Maidens (level 82)
Nigredo's Carrion Babies (number unknown)(level 20)
Aura's Magical Beasts (numbers unknown)(level at most 80)
Mare's 2 dragons (level 80)
Grant's children (numbers unknown)(level unknown)
Gashokukochuuou's children (numbers unknown)(level unknown)
*Demiurge's Evil Lords (at least 3)(level around 80)
That which lurks in the 8th floor (numbers unknown)(level unknown)
Head-Chef's & Sous-Chef's employees (numbers unknown)(level unknown)
Man Servants (numbers unknown)(level unknown)
Chief Blacksmith's apprentices (numbers unknown)(level unknown)
1 Lion Golem (level unknown)
2 High-class Golems (level unknown)
*Undead librarians of Ashurbanipal (At least 10 Elder Liches, unknown number of spirts and 5 level 80 Overlords)
*Summoned Mercenary Monsters (numbers unknown, but enough to bankrupt Nazarick in their summoning)(level 80)
72 Demons of the Lemegeton (numbers 67)(level unkown)
*1 Four-Colored Crystal Lamp (level unknown, but strong enough to wipe two level 100 parties)
And that (I believe) is everyone that is not a named NPC that was handcrafted by members of Ainz Ooal Gown. So everyone Ains considers not vital.
I could do more but I'm tired.