A spare set or power tubes and a pre amp tube are good things to keep in your gear kit. If it's an important gig I'd tote along a small amp as a spare. You can always mic it.
Just a suggestion regarding the volume going up since you'll be playing in a big hall ~
I'd suggest you keep it just like you always do, maybe even lower, but certainly not louder. People are going to attend the wedding and reception, you just happen to be there. Folks will want to talk and catch up with old friends and family. I suspect there will be people there of varying ages. Older folks may not have such good hearing. There's nothing more boring than sitting around a big table staring at people and not being able to have a conversation because it's too loud. I heard B.B. say in an interview something like "If you're shouting at someone it doesn't take long before they stop listening. But if you whisper something to them, they'll lean in to hear what you're saying."
Intensity without the volume is powerful. Anyway, just my 2 cents.
'Hope it all goes well and have fun