It's an interesting mechanic, and I like the idea that you can improve the drama by introducing a series of easy-to-kill "minions", which are mostly a one-hit kill.
If I were to use this strategy, I would be using the model of bourgeois of the Monster manual (S.345). you have one AC of 10 and only 4 HPs everyone. You can be from any humanoid race also. So you can use this as a base. Given that they only have 4 HP on average, it would rarely take more than one hit or attack to kill you. you Ability stats are all 10So you have a +0 on all your bonuses. They also only cause (2) 1d4 damage spikes. Therefore, even a large number of them shouldn't pose a major threat to an adventurous group – especially if you have group members who already have spells with area of effect.
I hope it helps.
The 1st level sleep On average, the spell should be able to take out at least 5 citizens. (PHB p.276)
A magic like fireball would effectively wipe out any number of Commoners caught in the area since the damage is at least 4 HP, even if they successfully completed their save rolls and you rolled all dice for 1s. (PHB p.241)