Requirements for adding CalDAV functionality to my app.

[localjo]

I'm building an app that puts events from subscribed webcal and ics calendars into a map. Prototype: https://github.com/localjo/CalendarMapApp

Due to limitations on accessing subscribed calendar events in iOS, I need a CalDAV server that basically serves as a proxy for subscribed calendars, to make them available on users' devices via a CalDAV account instead of as a subscription URL. So I need a server where my users can create an account, add their subscription calendar URLs and then log into the CalDAV account on their devices and see all of their subscribed calendars.

I'm trying to get a big picture idea of all of the technical requirements for building this, to determine what the overall costs would be and if it would be feasible.

Has anyone done something like this with Radicale? Is it possible to integrate this with my own app interface in such a way that my users don't need to know about Radicale? What would the costs of using Radicale in this way be? Let's say I get 100,000 users, how much does that end up costing to run? Are there any technical limitations that would prevent me from proxying a subscribed calendar with a Radicale server? Would any custom development need to be done to support this feature?

Thank you for taking the time to read, and for any suggestions!