Hey, a few responses from experience of living with a heat pump...
"Surface for the ASHP. Needs to be on concrete or similar." Ours is wall mounted.
"The ASHP makes a bit of noise - about as much as a washing machine." Our Mitsubishi Ecodan makes very little noise. Nothing like a washing machine.
"it was likely that our radiators would need to be upgraded to larger sizes." Possibly but we've had ours installed on our existing old rads with microbore pipes. They heat up pretty well! and over time we'll see if we need to upgrade any of them. Also with a terraced house you benefit from good insulation on both sides so it may be fine.