If you need OWP, I would apply right now.
For medicals, my wife was going to do her medicals before she gets her AIP, but when we called the medical office, they told us to wait for the AIP because when she gets AIP, she would also get some kind of form regarding medical check and it has reference number on it, which makes the case go faster once it's submitted electronically. They said, if we do the medicals now and send it to CPC, it would take longer time for them to match the medicals with the application.
This is just my experience.