What do I need to send the musician before the service?

If you use the Planning Center integration, EM sends the entire plan automatically — songs, keys, arrangements, and your service order. If you don't, send everything you'd give a regular team member: set list and keys, charts or chord sheets, call time, load-in and parking, what's provided versus what to bring, and dress. The more detail you send, the less room there is for error on Sunday.