You shouldn't lose data because your data is over 4GB. Yes, if you change to SQL Server 2012, you would lose your support. SQL will allow you a grace period past 4GB, but it is difficult to know how much that will be. But, at that point, you should have read only and no write, but you shouldn't lose data. It's not as if, SQL purges data and adds more.
There is also no actual reason to go with 2012 (although newer is usually better). SQL Server 2005, would be just fine. You have to remember, AC isn't that good with SQL support. I think you are very proficient with SQL, I can't recall. But, it isn't that easy to make an instance with anything but 2005 Express.
The other possibility is 2008 Express, which is free. It gives you 10GB of space but still only one GB of RAM. It would be really nice to have the unlimited RAM that most of the non-express versions have. Performance would be much better, and you could utilize that tons of RAM that a 64-bit OS allows.
