AI will be making my first wedding cake in March and I need help on what type of cake to make , with recipe (I'm at high altitude) and type of icing to go under fondant. If anyone has suggestions.

So, you took a wedding cake order without having any recipes...okay!  Why don't you google "high altitude (flavor) cake recipe " What icing are you familiar with? Crusting, non crusting, meringue? Out of a can? All can be used under fondant.

ADo trial cakes first. Test a few find one you really like then do that. I like to use a buttercream under fondant or even looks nice on its own. I like a buttercream with some shortening to hold its own and not melt and such. What type of cake are you looking for?