You are never alone on this forum. But yes not always all issues can be picked up on time especially @sam_nazarko is still busy sorting out some of the issues that where identified.
Your issue playing certain files leading to a green screen is quite special and might need to be investigated separately.
As this topic is more about your new device I would move this to a new thread instead of the 4.9 thread.
There is the backup tool in MyOSMC which also can be used to do that
Yes, if no network is working but you have “Wait for Network” configured (which you would need with your central DB setup there will be a delay for Kodi Loading.
Surely something need to be investigated (e.g. via terminal, which is your last point) but you could try to enable static IP to check if it just a DHCP issue.
Yes, check “Logging in Locally”