Hey Wiktor,
First, you really shouldn't use forever or pm2 in production. May I suggest you use something like Dokku[0] or Deis[1] (if you are planning to scale to more than one server) to deploy your apps?
Dokku is really quick to setup and will save you a lot of time and trouble in the long term. Setup takes only 5 minutes and the learning curve is pretty low (maybe 30-60 minutes to be productive).
NewRelic[2] and DataDog[3] are popular for monitoring though they're not open source. Nagios[4] is open source and also popular.
[0] https://github.com/dokku/dokku
[1] http://deis.io