Need some recommendations for logs and monitoring.

I have a mini PC that has a weird issue and occasionally reboots itself. So it's not usable for hosting any services that I strongly rely on. However, I'd like to use it for monitoring and logging. My current stable setup: - opnsense firewall - NAS - another mini PC - a laptop Can I use it to monitor and record network traffic that goes through opnsense. Or to collect system metrics, errors, logs, etc. of the other servers that I'm running? And which monitoring tools could you recommend?