Professional.Net is the plan I am using so here we go :)
Unicode: Unsure, is there someway I can find this out for you?
Database Size limit: The space your database takes up is counted as part of your Accounts space limit. So with Professional.Net you have 5GB total space. If your Web Site uses up say 1GB then your SQL limit is 4GB. To get additional storage its the same as with the web site overall: $100 for 1GB per year (a little less then $10/Month)
It does support PHP. I am running phpBB using a MSSQL Database, and the application installer will help you install it with a MySQL database. To enable PHP you use the DotNet Panel.
-Wilson Gearld Mead III
www.rangoric.com (Rather Blah)
blog.rangoric.name (Closer to Not Blah)