On the right side of the bike behind the side panel there is a 30amp fuse in a round black thing with a red and black terminal on it ( very close together i might add, surly if it rains hard these could short ?)....anyway what's it do please ?
Also behind the sub air filter there is a small row of vertical connectors.....blue, green, black i think....what do these do ?

The first one is the starter solenoid. It's the relay for the starter motor. I never heard of one shorting due to water ingress in that sense. If they fail it's usually because of the terminals getting corroded and going high resistance causing heat. If you are worried then lift the plug, clean it all up and insulate with silicon grease.
The electrical plugs by the air filter are for: alternator, side stand, oil light, neutral light and pulse generator. I think! It's a good idea to open them up, clean the terminals (especially the alternator which is the one with 3 yellow wires) , pinch the females a bit tighter and put together with silicon grease to keep corrosion out. You can remove any dodgy looking terminals from the blocks using a darning needle or similar implement.
You can substitute normal grease or vaseline for silicon grease but they are petrol based and may or may not eventually weaken the wires' insulation, which silicon won't do.