The rest really depends on how much tech fiddling you can expect from the audience. Obviously, just using a normal SSLed website has the lowest barrier. You would have the option of using Tor on the client side, but you could still access the thing with a normal smart phone if need be.
The next step up would be a site that is reachable only via Tor. This would (within reasonable limits) give users privacy of connection. However, if they exchange real phone numbers and other contact data - which they probably need to - this advantage becomes moot.
Encrypting private messages between two or more parties so the host can't read them would require users to keep and manage their own key rings. That's not a reasonable expectation. In any case, the most important content would probably have to be available to all users, such as client information for screening or a general community support message board.
I think with browser fully supporting P2P-WebRTC data channels it should be possibly to basically implement TOR as a website.
Notice though, I am by no means an expert on this topic, these are just my two cents. Also there will probably be a lot of problems in the implementation (node only active as long as website is open, which you could match with when the website was requested from the server etc.)
As I said I'm not an expert, so I guess the only thing I'm fairly certain about is that it will not be possible without Web-RTC.
[0] http://iswebrtcreadyyet.com/ ; no affiliation, just googled this.
[1] - https://unhosted.org
[2] - https://github.com/diafygi/byoFS
For those seeking simpler explanation of this look at [1], 7th paragraph.
[1]http://readwrite.com/2010/12/24/unhosted#awesm=~oIRyT1V2mrAL...
1. Run in the browser.
2. Would be anonymous.
3. Would use an anonymous host.
4. Would encyrpt every private message, and would have clear differentiation between public and private content.
5. Would have an easy option to download an extension to offer greater security.
6. Would enable average programmers to build sites with it.
Is there something like this? And if not is it technically possible and what are the technical challenges ?