Yesterday I hooked up the wiring following your steps @Wiltshire Chris with the same excellent results, thanks.Thanks @Wiltshire Chris x2. At least it was heaps better finding out about it in the garage on a winter day than speeding on a winding road at night in midst of winter (when skimping on antifreeze...).
Concerning the clock-A7, the safe bet is going via a relay. I was unable to think up good search terms for finding facts on the matter, so I ended up mailing Pioneer hoping they might respond (sometime soon)..!
EDIT:
Pioneer were quick to respond, they claim (no responsibility) their equipment only needs +12V for signal from A7 (ISO), so thin, low amp, wire would work. He wrote they normally suggest taking the signal from the lighter wire (switched on the b?). The rep had no issues taking the signal from the clock wire, pondering the possibility that it might affect the clock.
(I used Wago 221's (a double at the stereo and a triple at the clock)(!). Following the feedback from Pioneer I used a similarly thin wire as the clock wire and omitted the relay.)