I'm doing my first multi-tier wedding cake, covered in crusting buttercream. I will be adding lace appliques to each tier. I have several questions:
1. Is it best to use fondant, gum paste, a 50/50 mix, candy clay, or marzipan on a buttercream frosting?
2. How far in advance can I make these appliques and how should they be stored?
3. Should the cake(s) be at room temp to apply the appliques?
4. How far in advance of the wedding can I apply the appliques?
5. How should I store the cake to keep it fresh after applying appliques?

1. Is it best to use fondant, gum paste, a 50/50 mix, candy clay, or marzipan on a buttercream frosting?

   I have made dzns of b'cream cakes using straight fondant appliques and some w/ a 50/50 mix. 

2. How far in advance can I make these appliques and how should they be stored?

     The appliques can be made up to a month in advance (amd maybe even longer) but it depe4nds on how big they are and do they need to 'wrap around' the tier?  If the get hard/dry they will not so maybe a week at most for those you want to remain plyable.  You can coax them to say plyable by putting them in an air-tight container but that doesn't guarentee they will stay soft.

3. Should the cake(s) be at room temp to apply the appliques?

      I always worked on room temp cakes. 

4. How far in advance of the wedding can I apply the appliques?

    It depends on the appliques and how they are displayed.  I usually worked on cakes not much more than 24 to 36 hours ahead of delivery.

5. How should I store the cake to keep it fresh after applying appliques?

     At room temp, uncovered or boxed