Quite easy to calculate the current (ampere)
pump1 - 50W
pump2 - 100W
table fan - abt 20W
MH light - 250W
Some equipment has losses such especially ballast loss (in form of heat). So add about 30% to the MH light = 325W. Pump, at 10% losses. Fan no need to add anything lar.
So total wattages plus losses = 55+110+20+325 = 510Watts
Current (ampere) = Power (Watts) / Voltage (230V)
= 510/230 = 2.2A
So your timer or extension plugs should have higher ratings than this say, minimum 5Amps. (Give additional allowance about 1.5times of your calculated current usage). Will not heat your cables also.
Take not for those having chillers because chillers have starting current of at least 7-10 times the rated chiller current. So your cables, plugs, timers should be able to take the sudden surge of current for a few seconds.