If you need to keep data for 2 years I doubt SQL Server Express Edtion is going to be sufficient. It will probably be near the size limit. I am not sure if tests have been performed based on default Polling interval and retention settings, I wished I could give you an estimation.
Syslog and Traps can make your database grow quite quickly too.
Note the Express Edition has more than a simple 4GB restriction for the size of the database. It can use only up to 1GB of RAM which will limit the performances.