Ask HN: What do you use to monitor hardware in the field?

We are a B2B that has hardware running Linux in the field for a bunch of customers at their site (let's round to like 1000 machines and growing). All of them "connect" to our servers through OpenVPN and have been, from "days gone past", loaded with Zabbix and send us telemetry. Unfortunately due to personnel changes, no one is really sure of how things are done anymore and the task of maintaining this monitoring is coming down to me. How would you approach this task? I'm feeling a bit overwhelmed and reading online kinda want to just start over by choosing something newer like Prometheus.