Electrical – Do I have enough amperage in the service

I'm not sure where you live but US code calls for a minimum of #8 if you're using copper or #6 if you're using aluminum. There would be no advantage in using a larger wire size in this case because at 30ft you will have negligible losses.

I don't know what your voltage is or how many phases you have but for an example of what your losses may be, I will assume a worst case scenario - 100V single phase. If you used the #6 aluminum wire, you would have a maximum of 1.72% voltage drop (loss). If you used the copper #8, you would have a maximum voltage drop of 1.66%. And just remember, when you are calculating losses (voltage drop), the higher the voltage, the better because higher voltages have less voltage drop.

Note: I use the Southwire Voltage Drop Calculator for most of my voltage drop calculations. http://www.southwire.com/support/voltage-drop-calculator.htm

National Electrical Code says that you cannot connect conductors 1 AWG or smaller in parallel (310.10(H)). Since it's not likely that the conductors between your buildings are larger than 1AWG, you cannot do what you want.

What you can do, is install a new larger double pole breaker in the main panel. Then install a new set (4 conductors) of larger conductors between the buildings, to feed a secondary panel in the pool house. Then you can feed your branch circuits from the panel in the pool house.

The size of the breaker in the main panel, and the size of the conductors between the buildings will depend on what size service you want to supply to the pool house.