So i am doing my first three tired wedding cake this weekend and i need suggestions. My dh and I were doing an example last night of how it would go together and our idea wasn't working. He bought the spiked tiers so I don't need to use the bottom plates. Our problem we ran into is that we figured that i would just put the cake on the plate itself but when we assemble it the plan doesnt work. So now I am wondering if i should put the cake on a board and then just put frosting between the board and plate to hold it in place? Does this make any sense?

Yes, I always put my cakes on a cardboard the same size as the cake. After it is decorated I push the plate with the pillars into the cake below and then place the cardboard with the cake onto the plate. You can use icing between the cardboard and plate. I use some double back tape to put down on the plate first (just a small strip) then just put the cardboard on top.

I should have enough room for a ribbon and small border right?

If your cake is stacked (one cake on top of the cake below it) then your border would go on the top of the cake below it, and should cover the plate. If there are pillar between the tiers and the plate is the same size as the cake you won't have any room for a border. In this case you should get the plates 2 inches larger than the cake. (6" cake, 8" plate).