I would recommend MS SQL Server, not SQL Express. You will run into space issues in a couple of months, if not before that. Keeping historical data for 2 years will use up a lot of space, assuming you mean all historical data such as alerts, traps, and syslogs.
It would be advisable to start with a proper SQL server due to the fact youwant to store data for 2 years. You will hit the limit of 4 GB eventually and then need to upgrade the SQL. You will avoid additional steps when starting with SQL Standard or Enterprise.
I hope this has helped.