I'm making a 3 tier wedding cake plus 2 seperate cakes besides. All are to be covered in Fondant. If I make the cakes ahead and freeze them do I need to let them thaw completely before covering with fondant?

For best results, yes. Fondant on a frozen cake will condinsate and it will become sticky and you wont be able to smooth it down as well either if it's moist. Happy decorating!

I'd let them completelly thaw and come to room temperature before covering .. use a layer or two of buttercream first.. let that crust, then smooth really well and then cover with your fondant .. fondant will take on any flaws you have in your icing so it's always best to smooth your icing really well .. I swear by the Viva papertowel method for smoothing icing lol

I semi-freeze every single cake I cover with fondant with no problem at all. It is SO much easier than trying to cover and smooth a shifty cake!

Don't freeze the cake for days or anything, but 4 or 6 hours will give you a solid cake to work with. It's a breeze that way! Take them directly from the freezer to your work area and cover each one. They don't need to thaw at all first. You can smooth them easily. (See my photos...every fondant cake of mine is done like that!)

After you cover them and smooth to your liking, set them aside to thaw completely. A tiny bit of condensation appears...but it evaporates very quickly without leaving a trace or marks on your icing. Don't touch them or do any detailing at this point...let the icing dry and the inside come to room temperature.

Another hint...

After you trim the cakes of the excess fondant, let them rest on a smaller upside-down cake pan (i.e. if your cake is 8", use a 6" or 7" pan so that the cake's edges hang over) overnight or at least 8 hours. The fondant will settle completely as it dries and you can trim the edges again for a perfect fit.

Great tips Antonia.
I saw your cupcakes yesterday. They were amazing!