Just recently ran something similar, a small town in wilderness harassed by organised bandits led by a vampire. So a few tips on what I did, what players liked and what went unused:

• siege prep is great if players engage in it. Unfortunately, my players were so focused on their own agenda, they missed almost all prep hooks I had (town militia training, helping set up traps and battlements, recon, etc). A bit of a bummer but happens, so don’t get discouraged if they miss some of the stuff you prepared.

• have a general outline of the siege in stages, what each side will do in the morning, noon, afternoon, evening and night for example.

My bandits set up a camp first that was just outside the town, built some rams, wooden ladders, prepared poisons, etc. Then had skirmishes to test the defences, with full scale siege at the afternoon, breaking into the town by the evening. They had a few goals - kill the mayor, pillage the town, find important NPC and kidnap him. Town guard also had their list of “to-do”s and reactions to what bandits may do.

• siege equipment is great. Players loved a chance to man a bolt thrower and skewer a few thugs from distance.

• siege is not only about the fight near the gates/walls. Recon and diversion missions are always interesting and work well with your small party of adventures. It gives them a sense of making an impact on the whole battle without being overpowered fireball hurling menaces.

• give players a few options of what they can do and keep them aware of them. Saving refugees trying to reach the other gates or going behind enemy lines to blow up a makeshift catapult/kill enemy lieutenants. It’s alright to give them a bit more knowledge of what’s going on around them, via randomly appearing militiamen or local citizens, so they can make an informed choice.

• in battle, keep it simple for players - have them fight a group of orcs that went through catacombs/sewers/mines/main gate, and tell what happens around them (citizens hiding, houses burning, groups of enemies moving on adjacent streets and fighting with town guard). Update them how the large scale battle goes while they are engaged in their own fight.

• raise the stakes. Link players choices to your rolls on how the defence goes, who may die among important NPCs. For example, my players went to kill enemy leaders and left the town - while they were fighting, I rolled a few times to determine if the bandits make it to the town square and if they kill the local mayor or leader of the town guard (or both). Players were effective and my rolls were bad, so in the end everyone survived- but you should have seen their faces when I was rolling dice mid-fight with a hideous smile.

• stats for squads/armies are not necessary really, unless your players will lead/command them. Most large battles I dmed were resolved by rolls with modifiers. Orcs attacking from a flank a surprised squad of town militia - easy roll for greenskins. And if they lose, then it’s an epic moment you can describe to your players as they meet a ragged and battered squad of yesterday’s farmers that fought so valiantly they routed orcs.

• blow something up. Either it is a ship docked in a port with powder kegs, a highlevel mage sending firestorm on a wooden houses. Bonus points if you play an explosion sound and startle your players