1) You receive your OWP and you can show the representative at Service Ontario that you have a written offer for a job lasting 6 month or more
2) You are Approved in Principle (AIP), which is a step in the PR process that comes towards the end of everything. You can take the printed AIP letter and present it to apply for OHIP.
If you want to keep your private insurance, you should plan on extending it for at least 4-5 months, as that’s how long an OWP takes to receive (nevermind a job offer). I am in the same situation as you, but I never received an OWP, so I’ve had private Visitor’s insurance for about a year now 🙁