You can share with up to 5 people from FileMaker Pro.
To be able to access your data remotely you need:
1) A static IP address from your internet provider.
2) Forward the ports you need from your internet router to the host PC. It sounds like you only need port 5003 forwarded.
If your data is important I would suggest that you get FileMaker Server because it can do automatic scheduled backups. Otherwise make sure that you have a good backup plan in place. Note that you can't automatically backup a file hosted with FileMaker Pro, the file needs to be closed first before it is backed up. A backup of a file that is open in FileMaker Pro will likely be corrupted.