Assuming the wipers are already self parking, why not just fit one of the numerous electronic controllers which are designed exactly for folks like you.
Here's just one ....
Variable Speed Intermittent Windscreen Wiper Controller | Smart Kit 1093 -...
Heat pumps are intended for use within highly insulated properties, as with all heating systems they'll be expensive to run if much of the heat they generate is allowed to escape.
My final comment - the OP seems to be expecting to install a cheap system, expecting it to be cheap to run.
An expensive system to install is only expensive once, an expensive system to run is always going to be expensive.
wet rads, fed from a TS, which is heated via an ASHP will not normally need "an electric boost" provided you have sized the rads correctly, and assuming the house will be insulated far in excess of the currently BR requirements.
"the store will be an immersion" - this just tells me you don't...
Could you outline what your understanding of "the immersions" consist of please ?
Conventionally they are a resistive element immersed within a storage tank of water, which uses electricity as the energy source, to heat the water.
Lower flow temps to rads from a heat pump isn't an issue, you just size the emitters to suit (but I don't see anyone having suggested wet rads) just UFH
"Might consider air for the immersion heaters though"
You'll have to explain that one .....
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc