Hi @Arch9825 ,
I don't think that a guest user limit exists since M365 BS provides a Hub to collaborate on a Team that will mainly use Sharepoint to host documents.
So for each user, you add 10GB of your SharePoint tenant capacity and 1TB per user to One Drive Business.
Besides that, M365 BS can be used on tenants with 1 to 300 users only.
Some good references that can help you more:
Guests Collaboration
https://video2.skills-academy.com/en-us/microsoft-365/solutions/collaborate-as-team?view=o365-worldwide
Licensing Limitations Comparsion table
https://dynamics365now.com/wp-content/uploads/2021/08/Microsoft-365-User-Subscription-Plan-Comparison.pdf