One thought on your first question is to verify that firewall rules are established. See page 2 of my problems with installing the beta which could be similar to what issues you are seeing. beta 2018.3.1 install
In terms of your #2 question, I haven't solved this one yet, however I'm certainly interested in the answer in case you find it.
Firewall rules are established, hope no issues with that. Facing issue only when Im trying to access TSM URL if it become idle .
So you are not facing the unexpected server error anymore when you try accessing TSM? Can you try accessing TSM after 10mins? Because I used to get the error when TSM server is kept idle for sometime ~5 to 10mins.