Go to Tools/Startup and change the check boxes to what you want. Be careful with the Use Special Keys. If you uncheck it then you will have to write some code to get back to menus. Otherwise uncheck any of the other ones and hold the shift key while you open the database and Access will skip any startup procedures (AutoExec macro, startup forms, disabling menus, etc)
In order to filter on the Username, you will have to include the Username in all of your tables (or just the ones you want to filter by) and then use SQL to filter the results. Base each table on a query that has CurrentUser in the criteria for the Username field. That is one way to do it. There are certainly other ways.