Plumbing Questions? Ask a Plumber for Answers ASAP
Positive and negative head is decided by the highest water outlet not where the pump is sited. if it only comes in now and again then yes a negative head pump will be the better option.
to boost the whole house you need to connect it at the source of hot waterin your case the cylinder on the ground floor.
Yes of course if the taps are open the pump will or should run.
Hope this helps you in your decision making.Brian