Hey @%{original_poster_username,fallback:there}, welcome to the Nextcloud community 
your project sounds great!
While Nextcloud is open source and the sky is the limit as far as user numbers and scale are concerned, your use case is beyond the community’s scope.
The community forum is a community of volunteer enthusiasts helping and supporting fellow enthusiasts. The community has a huge knowledge base and there are some very clued up folks in the community who gladly share their knowledge and expertise in the spirit of open source.
Enterprise and corporate deployments are another ball game and require professional consultants, engineers and supporters who spend time and money gaining their expertise. These folks are certainly also enthusiasts, but their livelihood depends on that expertise.
Boundaries and limits are fluent and there’s plenty room for interpretation. As a rule of thumb you could say, from ~100 users you’re looking at a corporate instance and from ~500 users you’re looking at an enterprise solution and you’d be best looked after by the engineers, consultants and professional support at Nextcloud.
You’ll find community documentation and deployment recommendations here;
You’ll have access to concise expert documentation upon subscription here;