that is the cutest cake i have ever seen!
i say go for it, its your day, do what the hell you want to do!!!

i agree with using the colours too, as to not stress you out incase you cant get everything mario that you want.. maybe like.. red tablecloths with the big white dots (you could sew them on yourself!)
you could somehow make (or get someone to help you, depending on how crafty you are) table centre pieces using those flower thingys with the teeth.. LOL i have all kinds of ideas floating through my head...

you could walk into the reception to the mario music...