SharePoint in the Cloud - where is the best place to discuss answers?

Pardon if there is a better place to post this.

The community here at SevenForums is awesome! I am in need of a similar community for SharePoint, as I have a number of Cloud Hosted SharePoint questions, such as...

Q. Is there a limit to the number of SharePoint users I can have in the cloud? Someone mentioned 20k for BPOS and 2MM for Office365.
Q. How do you plan for scalability for a forum of 400,000 users on SharePoint?
Q. How do you test for that scalability?
Q. Are there design considerations that force an on-premise vs. in-cloud decision?

Can you recommend a favorite SharePoint forum, or is this the best forum to ask these questions and more?

I would think your best be would be to use Microsoft's SharePoint Products and Technologies Category

I use SharePoint on premise, but I am thinking that you will want to use something like vBulletin for creating a forum, not SharePoint.

Thanks, all! Gartner and Forrester report that SharePoint is indeed not a great answer and they compare and contrast vendor products. While I have not learned "the best" place to discuss differences, I have since learned many. If Social appears as a forum here in the future, I would be glad to contribute my detailed findings and participate in any discussions.