As much as you can afford in winter.... 4/3 steamer, booties, and even wettie gloves and balaclava if you want to feel even remotely tropical.
In summer you only really need a wettie to keep sun and jellies of ya, 1 - 2 mm, if at all
Other times i use a 3/2 steamer.
Some of the hard as dudes here wear a bit less, but im softer and prefer warmer