You and the love of your life have a choice to make, which would it be and why?
For the first two questions, the velocity of flow (2gh)^0.5. Flow velocity of flow * area of pipe (3.14*0.5^2/4). You have to subtract the head loss for the two bends and length of pipe. This is typically a loss coefficient * the velocity head, h v^2/2g. All lenth units in feet. To find the time, you need to integrate the flow vs. time equation.
The Big Bang was not an explosion that spewed galaxies out into the void. There is no explosion and there is no void. Thus there is no ahead nor any behind, because there is no line of galaxies flying away from any explosion. The universe is and always has been uniformly filled with matter/energy absolutely everywhere in space. All points in space are becoming more distant from all other points.
