Hi,
You have 2 problems going on. The worst one is:
An Error Occurred:Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.
Which means either your database server is under too much load to respond, or you are using custom code that is leaking connections because it doesn't close them and they don't get returned to the conneciton pool. I knonw that all mojoPortal code handles connecitons correctly so it can only be custom features or just over capacity for the server.
The second problem is that the /Data folder or some files or folders beneath it are not writable by the user that is the idnetity on the application pool. This may prevent users form uploading files and it may prevent logging of errors or writing to the search index, but it is the first error that is preventing your site from working at all.
If you don't have any custom code then you should check with your host. If you have custom code you need to fix the bugs that are leaving connections open.
Hope that helps,
Joe