Help me assault a mountain fortress

[Creamsteak]

I'm running a huge game (I've done it before, so I do know the concequences, and have prepared for as such). This is the "character cookie cutter" of a new series of sessions that will likely be called a campaign.

What you need to know:

I have the DMs resources to attack with.
The players are about 14 in number, all 1st level, and they will likely have 7 2nd level NPCs supporting them, and 3 3rd level npcs, and 1 4th level npc. They will have around 28 warriors with them. They have all the resources to withstand a siege, but this is a surprise attacks.

The players are not the brightest, and the fortress (albeit small) won't stand for very long without either insane luck, or some incredible unexpected skill, however I want that. The goal here is to see who (of the new players) is really into the game, and will get into this fast.

What you might want to know:
The setting is a renaissance era rokugan, with firearms as such from the DMG. The shadowlands control everything up to the worldspine mountains, and some of the minor clans are gone (the monkey, hare, snake, centipede). The major clans have all been shuffled in position by the lack of land. The world no-longer supports a happy courtly life. Now you see fighting on a toe-to-toe basis daily. These characters will be defending a fortress in teh Worldspine Mountains.

Here is the above layout for this. Imagine your "leader" for this situation is incredibly intelligent (think a lich Iuchiban figure) and if you want numbers, all mental stats are at least 25. However, his average troop has an intelligence of 3. His best might have 10s, but an average of 3.

So I ask for assistance in making this battle using a semi-realistic strategy.

 

[Kaji]

I'm hungry for more details!!!

Are the lich's warriors undead? And if the attack is a surprise, what about tunneling up from underneath? Hand those idiots some picks and shovels and say Dig!, have one of your intelligent leaders give them occasional direction, and next thing you know you have undead freakies creeping out of the kitchen.

I'm currently running a VERY undead focused campaign, so I'm always loking for new ways to use the little buggers.

 

[-Warlord-]

What about the foodreserves, and supplylines? Can the fortress take a prolonged siege? Do the villains have the time to siege the fortress for many weeks?
How about morale? are the warriors weary, or battleready? Morale is one of your first targets. Break morale and the rest will come tumbling down.
And what resources does the badguy have? Huge army? Small strikeforce? Any special troops?

Trojan Horse:
If any of the villains forces look human, let them knock on the gate of the fortress, announcing themselves as reinforcements.
Then when inside, at night, let them prepare for the attack.
Not only can they open the gates on the day of the attack, but they can sabotage bows, poison drinkingwater and such nasties.

A dagger at night does more damage than a hundred swords at dawn:
Get a single assassin into the fortress.

Hostages:
If possible, the badguy can overtake a nearby village, and demand the inhabitants of the fortress to surrender, or they die one by one.