The players really just have to worry about their 1 character. Meanwhile, the GM needs to come up with basically everyone else in the universe. That can be rough, but there’s things to help. Limitless Adventures is running a Kickstarter campaign for one such book. It’s their Limitless NPCs Volume 2.
From the campaign:
We’ve created 100 new, highly-detailed, NPCs for your dnd5e game. The NPCs are divided into four categories: Allies, Contacts, Foes, and Merchants. Each NPC comes with a full 5e stat block, pre-rolled treasure, and three adventure ideas. Each NPC is setting-neutral, and can be dropped into any 5e fantasy game world.
20 New Allies – Adventurers with different skills to round out your party. Allies will join the party on their quests.
20 New Contacts – Similar to an ally, contacts will provide assistance to the party, but will not put themselves in harm’s way.
10 New Scaling Foes* – Every party needs a good enemy! Each of the foes included in this book come with four different versions, one for each of the tiers of play. This means that our foes will scale and grow with the party and provide a challenge at any level. (* 40 total foe stat blocks).
20 New Merchants – Shopkeepers of all kinds, each with a detailed chart showing their wares and prices.
300+ Further Adventure writing prompts to inspire your campaign. Every NPC has three quest hooks, motivations, and other ideas to help you write your game world. Perhaps they have a secret goal, need help with their own quest, even foes might be convinced to lay down arms or change sides.
The campaign’s over 3x funded with 20 days left to go.
Source: Tabletop Gaming News