I'd say go with the waistcoat, and PC, shipmate. Also--do you have a Navy tartan (Edzell, Polaris, SeaBee) or if you served in the USMC, a Leatherneck tartan? Typically to navy related functions, I choose to wear my Edzell first, however mine is not formal--so then I go with clan/surname.

I'd also leave the mini-medals behind. Just my opinion. I don't wear any military medals in civilian attire. I know some people do and it's your choice--but I just don't like it nor do I like seeing it at functions.

I think the plaid would be a tad 'much' as well.

Just the opinion of one sailor