Hey Leigh - not everyone left. I'm still here!
As for the size of gun - an 80 - 90 cm is about right given the species of fish we have and the visibility we deal with. I use a Riffe Comp 0 and it is perfect.
As for wet suits, 7MM is standard if you want to stay out any length of time. Riffe makes good suits, Mako suits are probably the best value for the dollar, but what ever you get you want nylon on the outside and unlined on the inside for maximum warmth. You will need suit slip to get it on.