Which version to use and if any vulnerabiltiy

[Abinash]

I want a suggestion on which database to use : mariadb or postgresql???
Which one would be the best for longer run and around 2500 hosts?

[Rudlafik]

If you want smart monitoring like Dynatrace then ZBX is not the right way. They are mostly commercial systems. You can get remotely close to it with correlations, predictions, but only after you collect enough data in cycles given by the measured system (day, week, month, year?) You will also need a perfect analytical tool for logs, I don't know if ELK is the right way. I would personally choose PostgreSQL and TimescaleDB addon for DB.
Moreover, if Prometheus and Grafana wouldn't be better for your monitoring.