Is there a node network explorer or some kind of overview page ?

Yes, there is:
Link above is an early analytical page for node related decentralized network statistics. Currently it provides:
  • Presearch Network Status - Insight into number of nodes in each of the Mainnet regions and Testnet. Also provides number of active nodes over the world (per country)
  • Daily Search Statistics - Values are providing a sliding window of last 24h per metrics of # of Total searches and # of Guest searches executed as well as # of Usage Rewards allocated