Hello @MickeyBlumental, this is currently a known restriction that the NPC characters would be using the default collision size of the Fortnite Character, the engineering team is aware of the restrictions and working on supporting customized size in future updates.
Regarding your ask about the tutorial, could you check the Verse Starter Template | Epic Developer Community (epicgames.com) documentation? It should answer most of your questions on on the template was built and you’ll also learn how to apply similar mechanics to your own experience.