Mark. I believe your water supply is inadequate because of grossly undersized supply pipes.
With a 450ft supply pipe & static head of 110ft your minimum supply should be 50kpa 7lb at the most disadvantaged outlet/with all outlets open. In Australia the minimum sized pipe for supply purposes would be 40mm or 1,1/2″, I would install 50mm or 2″.
I also believe you are correct in that if you install a pump it will provide negative pressure in the existing 3/4″ line because of friction. if you were able to suck enough water through the pipe you then will also have a flow velocity within the pipes exceeding 3m/s or 10ft per sec.
Is it possible to install a tank that can be filled through a ball valve from the existing supply pipe & then pump from the tank to your house?, If you can, may I suggest a constant pressure type pump or a pressure limiting valve to equalise pressure to your upper story.
You will have to do the siphering to work out the cost differences between a good quality pump & tank including associated plumbing costs or alternativly replacing the 450ft of supply pipe.
However it seems to me that the builder may have been grossly negligent in the installation of a supply that was inadequate for the purpose it was designed to serve, after all he is a professional?