OHIP you get after 3 months after doing your arrival.Some people are saying that OHIP is covering everything from day1 but I am not sure, check online. I would suggest to buy an insurance at least for your wife as OHIP does not cover everything such as dental, eye, physio etc. I am not sure how all these may be important during pregnancy.
Do not apply SIN online. It is taking to much time. Go to service Canada after your quarantine is done. They will give you in 10-15 min.