Will be interesting to see what their initial suggested heat curve is (have had a play around with an online calculator so I have my own opinion). The designer was very patient when we were having back and forth discussions on which rads to swap, at which sizes, based on achievable flow temps. 

A shame that it sounds like the external temperature sensor is wireless (and therefore needs to be somewhere I could change the batteries in). Fitting on the north facing wall will mean that it is quite high up (given the roofline), understand that west facing is also acceptable?

Your installer should show you how to operate the system, but you should also ensure that you are shown details of how to make adjustments to improve efficiency.

I've already got down on my list in my head to take some photos of the 'plant room' prior to the lagging going on the internal pipes (is located in an unheated garage)  

Thanks in advance!