1. FMP has to be running in order to host the file, so yes, a user must be logged in. That's not the case for FileMaker Server FYI.
2. Not sure about the CPU usage, but you should definitely exclude the folder where the live database file is from your backups. You NEVER want to back up a live database file, that's guaranteed to corrupt the file.
You need to implement a scripted backup routine, or install FileMaker Server, which handles backup schedules for you (and would be a more solid host). For IWP you'd need FMS Advanced.
FileMaker Server is not cheap, but what is your data worth to you?
You may want to consider a professional FileMaker hosting provider, such as ourselves:
We host on FileMaker Server Advanced and provide the server licenses, hardware, monitoring, upgrades, etc. all as part of our monthly rates. Feel free to contact me here or off-list at jmay(at)pointinspace.com with any questions.