The RAF output from all American schemes (Arnold, Towers, Pan-American & BFTS) was:
Pilots - 13, 673
Navigators - 1715
Wireless Ops/Air Gunners - 662
(Source: Public Records Office, Kew as mentioned by Jack Currie in Wings Over Georgia)
Plus, of course, there were the aircrew graduates from training schemes in Canada, Rhodesia and South Africa.