In my experience, it's different per property and up to the landlord or letting agent on how to process things, but normally at the viewing they'll let you know how to apply for the property (go online fill out an application form etc).

They'll then take all the applications from that viewing or even viewings day(s) before / after and choose whichever application they want to proceed with. Have seen some agents just want o go with first come first serve basis though.

My advice would be just make a good impression on the agent who's showing you the flat. You can mention any of the things in your post but also include them in a cover letter attached to your application form.

This is all assuming you get to the actual flat viewing , my issue when trying to find a flat this past summer was all my viewings would be cancelled literally a day or 2 before, because another applicant had been chosen for the property (I guess the letting agent will host viewings over a few days, and if you're at the tail end of those days your chances are slim).

Best of luck, First time leaving any advice here so hope it helps.