1.5mm - 2.5mm should do, but do you have a total wattage of everthing?

Also the length of run of the cable - the longer the run the larger the cable has to be, but it depends on the the total wattage / volts / length of run, there are tables to determine the volt drop per meter of cable.

Also please post what cable you plan to use as different cables have a different volt drops - but the main thing is the total wattage, the voltage and the length of run of the cable.

The pump and Mister wont have a large load (wattage) but the light might have a large load.............best thing is to post back with the total loading of the cable (total wattage and the voltage)