What function will this server provide (File and print server, Opera Application, Opera Database, both Application and Database).
If this is going to be used as the Opera database server you should look at getting 15k drives rather than 10k drives. It will be more expensive but if the intent is to use the server for the next 5 years it will be improve performance for your staff accessing Opera.
Also, I would purchase the windows 2012 license but have them install windows 2008 R2 – as Opera is only supported on that OS – it has not been certified on Windows 2012