I think it's better uploading the medicals and PCCs before CO asks for them. Your application will be delayed for at least few days or weeks if you wait to submit them until CO allocation. About the Form 80 or any other such forms, I think it's better to wait till CO asks as CO may ask for different forms according to the country you are residing. If you log into your immigration online account, there is a way to auto generate HAP Id which I cannot remember exactly how. Please note all of these as per my application experience and may differ with your case. Wish you good luck and a speedy grant .