I'm making my first wedding cake, 3 tiers covered in fondant. Does it need to be on a cake board if I am using a base or put it directly on the base?

I would put it on a board first

I after reading the question again... I wanted to know if the cake is going to be stacked? If so then if you are using the sps then I have done it but there is always a board first and I put it on my decorative base but they are just a flat base. What kind of board are you using?

Always put a wedding cake on a cake board then place that on a base. You do this for a number of reasons: First, when disassembling the cake and cutting it you don't want the cake base scratched up. Second, if you look in my pix, the towering inferno cake -- that was on a cake board on a plateau and at the reception hall they lifted the entire cake off the plateau to take it back into the kitchen and cut it. They couldn't do that if it didn't have a board underneath it.

Not only that but for sanitation reasons, you wouldn't want your cake to touch a metal base, (I'm guessing your base is metal so it may not even apply to you,) and also you need your bottom board (in my case I iuse foam core boards,) to hammer my large dowel down the center the bottom board is part of your support. Not only that it just looks nicer!