The calendar on my server is empty. Whenever my computer syncs with it, the client warns that all my events on my computer will be deleted if I continue to sync. How do I upload my entire calendar to the server, using my client calendar as the base, not the server (empty) calendar?

You need to disable the client in System Preferences and then re-enable it. Once re-enabled reselect the groups and calendars you want to share with others.