Shasta - love your story!
To guest parent - Surely the wisest thing you can do for them is to give them an honest review of your own marriage, with your personal answers to the questions you posed. If her parents can do the same thing too, the pair of them are already better-advised than most young marrieds
As to pre-wedding advice: While my Dad and I waited behind the aisle, he whispered "Don't forget you can still change your mind, I've got my car keys". This is absolutely the traditional thing for the bride's father to say (makes sure the bride knows she's walking down that aisle by choice!) but I have no idea what fathers of the groom say at the same moment
Cheers. Have a great day.
AG