A word of advice from personal experience.
Start with the simplest possible setup, so you are only dealing with one thing: an empty project with no routing, and no busses set up in Audio Connections, you can add them back in later. Use an empty project, not a template. Don’t create any new tracks yourself until after your test succeeds completely.
There are two ways to login: The My Steinberg login Name/Pass and and the Id login. Both do work, and I generally use the Id login with Name/Key instead instead of Name/Pass, because it does not depend on the performer having a My Steinberg account.
If you have a VST Connect Pro license, and are connecting on the LAN you must not login. Instead the LAN Connect icon lights up blue, and you click to get a connect menu.
You do need to have a good understanding of how the sequencer works, particularly regarding cue sends , and the Control Room. Look up any other jargon you might not understand. A reading of this forum reveals this to be at the root of those chronic headaches. 
Use the Create VST Connect menu item to set up the routing for the system, don’t do it yourself. And, do not do any manual tweaking before you establish a working connection with the performer and have tested talkback, talkback/rehearsal mode, recording and the cue mix
Know that there’s little that can actually be troubleshooted. a good thing to do when it does not work is to use the VST Cloud menu item, "Remove VST Connect’ and then recreate it using the ‘Create VST Connect’ menu item. It takes only seconds to set the routing up.
Thanks go to fuzzydude for some of these details