Looks like a lot of work to put together, but compared to the time spent manually watering its a great time-saver.

Do you find the plants closer to the barrel get more water than the ones further away I wonder? Suppose you could block some extra holes there to increase the pressure at the far end.

In terms of checking your water level, you could make a float from an empty plastic bottle and tape a stick to it with lines for level, would save you climbing up all the time to see whats going on? You have rough thirds on that barrel already for approximation.