we have just purchased a shower panel, which has multiple outlet jets

The instructions suggest a minimum of 1.5bar, recommended 3.0bar.

The shower panel is to be mounted on the ground floor. The water system
is conventional gravity fed, with the cw water tank mounted above the
ceiling of a three bedroom town house.

Would you recommend a pump is installed ? If so which one? Would you
recommend a single impeller, with the cold fed from the mains and the
hot fed from the cw tank (via the hw cylinder !) or dual impeller, with
all water from the tank ?

thanks