Profile Field Dependencies

There isn't out-of-the-box support for that, but widgets that render them (by default, the User Profile Fields widget does) could be updated to programmatically address this.

Would that be using Velocity? I would need some guidance with that.

Yes, this would be a combination of Velocity and JavaScript. Before developing, I'd recommend browsing the Developer Training, especially UI Customization and Scripting.

I was going to use ASP.Net MVC to develop some of these features using the APIs. Do you know if this is possible?

This wouldn't be a directly-compatible approach. Community has its own supported stack for rendering UI in the form of themes and widgets, which are then made configurable to non-developers.

That said, you can consume the REST APIs from any platform/stack you wish. But if you're trying to build user interfaces, you'll want to use widgets.

Not all my requirements are minor user interface issues. Some of them have to do with accessing the database, etc e.g. this one https://community.telligent.com/community/11/f/ask-the-community/1147512/verify-email-addresses, so I think I'm going to need more at some point.

Understood. I recommend reviewing the developer documentation. Custom plugins will perform the heavy-lifting for functionality (whether that's DB access, etc) on the server-side which, in turn, expose custom APIs to widgets and themes in the UI. Community, itself, is built on these same supported extensibility points.

Okay, thanks. I will review the docs.

Okay, thanks. I will review the docs.