I would greatly appreciate any advice on what size pressure pump to install to run the main house water - both hot and cold feeds. The pump will be installed about 20' away from a large water tank and about 4' below the tank outlet. The feed to the house would be about 25' away and head height would be 8' up to house floor level, then it needs to run to all the outlet places in the house...kitchen, bathroom, laundry and two low flush toilets...and LPG gas instant hot water system.

I also read once that if you install a larger pressure tank than what is the norm, this saves power usage as the pump doesn't need to turn on as much...there appear to be some logic to this but not sure whether it is advisable? This is of interest as I am on stand-alone solar power 4kw system.

There is only two of us living in the house normally.
Inlet/outlet of pump would be 1" I would assume...1/2" piping is generally used for hot water and 5/8" or 3/4" for cold water feeds.

I am not sure whether you need more info but hopefully the above will get something going?
Many thanks