I've cracked the first part of the puzzle - here is a screenie of Supermarine Walrus spawned from HMS King George V. Not the most exciting, but proves the concept:
Ignore the Illustrious Class and the Swordfish in the view - they were for testing purposes and not attached to the battleship.
Unfortunately it comes with a price. Aircraft will only spawn from a type 8 (Escort Carrier) or type 9 (carrier) ship and I believe this is hardcoded, so unless h.sie wants to dig onto the code (or someone can tell me otherwise) it means that if we're to have spotter aircraft from battleships then I'll have to rewrite the _SCR and _RND files to reflect the new ship type. Unfortunately, that means that I'll have to write bespoke campaigns for each supermod, reducing the accessibility of this mod.
It would be great to see a spotter aircraft (from my research I believe that there was only one type used by each nation - a good indicator of capital ships being in the neighbourhood!) but it's a trade-off between that accessibility.
Can anyone prove or disprove my theory?