Air source heat pump - which one?

I am specifying air source heat pump for a 230 sq meter new build.
The heat pump will be fitted directly next to heatstore or hot-tank with just the outside wall in between.
Any suggestions as to which heat pump is the best one to fit?
The Mitsubishi Ecodan 14 KW seems to be pretty good??
1. Would I have more control by feeding UFH via a heatstore or is it best to feed UFH direct from the heat pump?
I have been told by one company that as the UFH pulls low temperatures off the heatstore, the heatstore will last for long periods and can be topped up with the heatpump using economy 7/10 cheap rate electricity.
It can even be set to minimal temperatures at peak times (expensive electric) and top heat store up during cheap rate.
Also a HS has immersion backup for both hot water and heating if necessary and has faster recovery for hot water because the heating also heats the HS.
Other points, I have been told, are that the heat pump will run for longer periods increasing running costs if done directly to UFH and the possibility of re-cycling.

2. I shall have economy 7/10 electric tariff for an Aga, so is it an advantage and possible to set timer/temperature to top up on cheap rate and set minimal temperature on full rate for UFH? Presumably there is no problem controlling the hot water heat up time to cheap rate!

3. My main point is: As I will have cheap rate electric tariff, would it be advantageous to fit a heat store to serve both under floor heating and hot water or should heatpump feed directly to UFH??

I would be very grateful for your views

Steve