Hi,
From my own experience, and from what I've researched online, getting all your paperwork together when submitting the visa application is advisable. For instance, getting your police cerificates in advance means that when they do review your application your case officer won't need to request these (potentially adding a delay). However, I didn't get a medical until after submitting my application. I received a message to organise this about a 2 weeks after submitting my application. So you could do the police checks before and then the medical after? You can do the medical before but I am not sure how they submit your results to Immigration without an active application (hope that makes sense). The only potential issue is that you get your police check/medical now and due to processing times it takes 12 months to get your visa. Potentially, your certificate/medical could have expired meaning you need to get anothet one. There will definitely be accurate information on the Immigration website though. I found the FAQs section really helpful.
I am not familiar with family applications but again, the website will have everything you need to assist the process. Also, there are a few immigration agents on this forum who are great at answering questions.
Cheers