First time DM working on a map of the starting area for the party (they'll arrive escorting a caravan) and would love some feedback on my opening plans. Plan is for this to be a fortified settlement of 1200 citizens (would have 20 guards and 80 militia as it's a more militarily located and focused settlement)
Upon arrival the party will be at the rear of the wagon and some of the guards at the front of the caravan will turn out to be Zhentarim slavers. They'll slit the throat of the merchant, cut the hitch for the horses and cause the wagon to be stuck blocking the gates from closing, then attack the gate guards and the party while one of them blows a horn to signal the main force to attack.
At the same time, loud shouts will erupt from the woods as about 300 Zhentarim slavers emerge rushing the gates. The party will have a certain number of rounds to deal with killing the fake escorts and helping the town guards to clear the wagon from the gate before enemy forces reach the gate and rush inside.
My plan is to then have the party either help defend the settlement during the siege, or be part of a small group that exits via the north gates to take horses and ride off to call for aid.
If they remain in town for the siege I plan to have the slavers offer to spare the lives of the townsfolk if the town surrenders and gives up 10% of the population as slaves. The leadership of the town will reject the offer, but some townsfolk fearful of dying will form a mob trying to open the gates and take the deal.
The party would have to either negotiate, intimidate or fight some or all of the mob depending on how they approach the situation. They'd also have set pieces where the besiegers make attacks on the town and they'd be involved in throwing it back long enough for outside help to arrive.
If they opt to be part of the small group that rides off to call for aid, they'd have encounters along their route with slaver scouting parties attacking them or coming across slavers attacking others on the road or escorting captured slaves, etc.