I am doing a three tier cake - for 50-60 people. It will be stacked. Do you think I can use just the small wooden dowels, or should I put some of the bigger plastic ones in the bottom tier? Thanks. Any suggestions welcome.

several (4-6) in the bottom and middle of the tiers would be required. Usually, the small wooden dowels work fine. If you think it won't be supported well, add another dowel. It depends on how deep the layers are and how heavy or light the cake is after it is bakes.

As long as they are all perfectly level, it should be fine.