My cousin asked me to make her wedding cake. I have made a four tier cake before, but the bottom layer started to cave. should I have a thick base for it not just cardboard. should I put dowels in every tier?

I believe the rule of thumb is for every 4 inches of cake you need dowel rods and a seperator board or plate placed in it. I made this mistake years ago before I done cakes much and the bottom layer caved. I had never put together a 3 tiered cake before and learned my lesson from there! I also add a piece of wax paper between the board and layer also to keep all the icing from the bottom layer from coming off on the bottom of the upper layer. I hope this makes sense. lol

Use a cake drum as the base board and SPS for support.

You definitely need some type of support system (i.e. SPS, Dowels, bubble tea straws, etc)