Hmm interesting, the Event XS (thermostatic) they show could in many ways be a easy install for you. It is as you susspected a shower with its own pump built in. The pump is housed in a case not unlike your existing electric shower. Hence it could be installed using the existing power feed (via a FCU) as well.
Yup, and yup. The only disadvantage I can see is that it will not boost the pressure to the bath taps in the same process. In fact if someone turned on a bath tap while you were in the shower it would probably just "steal" the water before it gets to the pump.
Hence I would be tempted to go for the separate pump and place it in the hot and cold feed before the bath taps. That way the pump will run when you use the shower or fill a bath. It will also mean much greater flow rate is available to both shower and bath.
2.5 is pretty poor even for an electric shower... you could get upto double that with a good one ;-)Well if your stored water is at a temperature of 65 degrees, then you will be blending it about 2:1 with cold. Hence that will give you over
11 mins of showering with the pump running full tilt. In reality you may well find that 8 lpm will still give a decent shower and extend the running time to more than double that (given that the boiler should have noticed by then and set about heating the water while you are still in the shower)The pump will require far less power than the existing electric shower, so the supply for that will be far more than adequate. Having said that you may find it simpler to add the shower pump somewhere else anyway (like next to the hot cylinder in the airing cupboard).
Double pole refers to a switch that opens and closes both live and neuteral, rather than just the live. Thes switch on your shower is almost certainly double pole.
Nope, you seem to be going in the right direction.
Have google on previous threads in this group. Andy Hall has posted in the past about a good shower pump that may suit your needs. The Mira showers you are looking at are nice, although quite pricey. You could probably get away with a simpler bar mixer type. (I bought a cascade thermostatic bar mixer complete with shower, and rail etc from Makro recently. Cost was 49+VAT).