Gemma- If it is your first time delivering such a large cake- i would stack the last 2 tiers on site- leave yourself enough time to complete this at the venue- be sure to bring all necessary supplies and a repair kit.
I would not do a tiered cake without using the SPS system- they are very affordable, I get mine from Oasis. I think there are you tube vidoes on how to use them- one important step is to make sure you place your cardboard cake board on top of the sps plate so that the point pokes a hole in the cardboard- I usually make that hole a little bigger before I place my cake on top.
Good luck
