The startups in FounderCulture do a lot of offsites, and we have some pro-tips on how to plan a great offsite.
The link above includes:
An offsite Notion template from The Unicorn Project that you can duplicate and use for your offsite
Advice from Startup COO Sue Odio on how to plan great offsites (15 minute video)
Specific ideas for your offsite.
We also have other specific vendor recommendations page with vendors that we have used and trust to create great offsite experiences.