Carrock

It's possible that most ETs have calculated that sending out, say, a terawatt of 'I am here' signals for a million years would give them a 50% chance of contacting one other ET civilisation. They may not be advanced enough to take the long view.

Spin polarized monatomic hydrogen has been the rocket fuel of the future since at least the 1950s. I don't know the specific impulse but it is pretty high. It's nowhere near as easy to handle as nitroglycerine and it requires a liquid helium plated fuel tank as it reacts explosively with anything else. There are a few more similarly trivial problems to overcome before it comes into use.

There's actually a lot of practical value on the moon. There's water that can be electrolysed for rocket fuel and at least most of what you'd need to manufacture spacecraft. Only about 3% or less of the energy required to launch an interplanetary spacecraft from earth is required to launch it from the moon. You could even build a linear accelerator to launch spacecraft using only electric power from ( a large number of ) solar panels. Of course all this would require an enormous investment before there was any payback. Science fiction would be pretty dull if authors ran their ideas past an economist.....

It's not at all clear how long inflation continued ( perhaps far longer than the minimum required to fit observations ), but at the end of inflation the (now) observable universe was certainly very small. However it seems likely a much larger volume at that time was very similar to what we can see - no edge effects have been detected. It could easily have been more than 30 billion light years in diameter back then. Enough to qualify as a big bang?