You can merge and compress PDFs all in one, just make sure that they are readable.
Attach translated documents and original copies without any stamps of translators.
Yes, you need to attach all of them. Non-translated documents might not be considered by VO at all.
9 is not a lot at all, people attach hundreds of documents.
Visit visa is nearly impossible to get for parents. It's better to apply for super visa.
Marriage certificate is required. You can try to upload a letter of explanation. But what is the problem to get it?
Try to call IRCC, re-reply them again to all the VO.
Use @cic.gc.ca at end
cic-calgary
cic-etobicoke-landings
ircc.clientportalhm-mhclientportal.ircc
ircc.clientportal-portalclient.ircc
ircc.clientportalprairies-prairiesclientportal.ircc
ircc.clientportalontario-ontarioclientportal.ircc...
You can add him any time later before the COPR, you still have time. Your application might take 6+ months and there are many ways to make it even longer.
Visitor shouldn't mention any other reason than a visit. If you do that what you plan, he will be definitely refused.
You can add him to your application, but you need to prove 12 months of cohabitation.