Put in a similar layout in my bathroom 30 years ago but with a Mira Event. Took the hot feed from the vent pipe near the bottom of the hot water cylinder on the assumption any air bubbles would float upwards before they got near the take off. Went up into the ceiling, about 2m across for 4 m and down 1m into the shower. Cold tank in the loft about 1.5m above the shower directly above it. Minimum required head was 80mm and necessary to make sure the pump actually primed. Only issues I have had is when I fill the bath and it empties the header tank and hot water pipework below ceiling level whence an air lock is formed in the pipework along the ceiling. I sort this out by putting shower hose on floor of shower, run shower and this clears air lock after a minute or so. Have replaced motor brushes once.