Munin can be used to monitor the following parameters:
Disk space usage
Number of SQL queries
Munin setup documentation: http://guide.munin-monitoring.org/en/stable-2.0/
Web URL availability can be monitored by external services like ServerGuard24. Just setup HTTP checks on the web port and TCP check on data port. Since PowerFolder can be slow sometimes, it makes sense to set a timeout to 30 seconds.