Step 1: Execute Prisoner. Step 2: Eulogy. Step 3: Repeat Step 2. Step 4: Profit!
Never give up, never surrender!
The only time a location must be played within 2 of a reactor is when you need to pay the energy requirement:
page 3 wrote:
This energy requirement must be paid by a location in your Space Station with Energy Cubes on it and within 2 distance of the location you are attempting to build.
All other locations can be any distance from a power reactor, so long as it is adjacent to another location.
As for your second question, as the Main Reactor counts as a Power Reactor, I would say yes.