This
Navy News story from 2003 suggests that 17 was the record.
Harrier launch record claimed by HMS Invincible
Also on board were nine FA2 Sea Harriers of both 800 and 801 Naval Air Squadrons, adding to the organisational challenge – not least in how to arrange 17 Harriers on the flight deck and in the hangar.
Post SDSR, we facing starting this from scratch later this decade! Hence the link in my above post.
Regarding your seond question, I don't think a V/STOL AEW type was ever considered feasible.