Should I wait before creating scenarios?

No worries James, I did not take it as a criticism of the route. We've sometimes found that a scenario can just go "bad" for whatever reason. If you want to try again start completely afresh and just put the player train in. Get the time of day and weather set. Make sure you can run your scenario and put all your instructional text messages in before doing anything else. Then start adding AI one train at a time using inbound portals if at all possible. You can start AI trains in the platform at terminii, but no others.
Then if it goes bad, it's the last thing you did causing the problem. Keep the faith and I'll send over a copy of the scenario creation guide as far as we've got in a PM to you. Its by no means complete, but it'll get you off to a better start.