For anyone interested, I fitted the pump over the weekend and so far everything's great.
In the end, I decided not to fit the pump above the hot water cylinder, instead I've effectively extended the bottom half of the airing cupboard sideways to allow me to fit the pump next to the cylinder. This meant I didn't need to worry about the AG loop and was able to replace the existing fitting with a Warix flange rather than drilling a new hole for an Essex flange.
The pump is raised off the floorboards with a few small lengths of 3x2 and sat on a piece of 8x1. It came with large foam pads which the pump sit's on to minimise vibration and noise transferrence.
Never having used it before, I was a little wary of using plastic pipe, but I found it extremely easy to use and to bend and had no problems whatsoever with any of the connections. I think in future I will be thinking plastic first as it was so easy to use.
I've put the hot water supply for the entire house onto the pump and have noticed a fantastic improvement already. It used to take an age to fill the bath but took no time at all last night. Not had a chance to test the shower properly yet as I still need to fit the shower enclosure(next weekends job), but at least I know I've no leaks.
Thanks to everyone who offered advise.