Once you have these admin pages in your site you should definitely apply security to them to ensure that only allowed users make edits to the data. Like you said using Security Assist would add in this security for these pages. There is nothing that you need to do to these pages before using Security Assist. You will just use the wizard to generate the pages then you can apply the 'logged in' access rule to the admin pages that you want to protect. It is also common to have these protected pages in an admin directory to help keep it away from the other parts of the site.
As for using UE4 or Digital File Pro to add upload functionality nothing needs to be done first, you can just add it into the pages after the fact.
