Mission 4 is when you get "onslaughts of troops" from the Rat.
I went a bit mad here...
This screenshot was taken just before I got the VICTORY sign =3
Taxes were mean and rations were double.
(sorry about the qualty - had to drop the filesize because GOG doesn't like big images =( )

you wait till you have 100+ archers and crossbowmen ;) :)
now that is overkil

Sounds fun :>
/me replays Mission 4 heh heh heh heh

Huh, interesting. I got through that with only about a dozen troops, if that, using a much smaller base - building your perimeter wall that low wastes the height advantage, without which I'd have probably been massacred. I've found that double gates are useful, too - you can stand archers on both, and if the outer one is breached, pull your men back to the second while the others protect them. It works best if you set up your base so that the mountain itself forces your enemies to approach the gate, not just the stockade.
I'm still getting the hang of rush building a base, so I've relied on a tiny handful of soldiers and a bit of help from some passing woodcutters so far. I'm impressed at the army you've raised there!

One other thing in Mission 4...
If you place your keep near the rocks in the center (to the left in order to take the height advantage) you can place troops on the roof of the keep. The keep is much higher than the gatehouses so they can shoot farther.
The keep is usually is "the last stand" on difficult levels; It is always advised to keep a few troops up there to be the final protection of your lord if your walls are breeched. But, there is no reason why it can be used as an offensive tower either. (Though I would not attach it to an outer wall, especially in later missions.)