SQL BackUp using Maintenance Job-Collection of common programming errors

Microsoft SQL Server 2008

I am almost completely out of space on my main C drive, and would like to backup to a secondary local disc. I have a maint. plan set to do so, but have a couple questions: 1. I chose “All user DBs” options. Does SQL do 1 by one, or try to do all at the same time? 2. Will backing up cause temporary files on C and therefore max out my drive and crash the server?

Thanks!