pad152,

Like Mad Daddy said you don't need to create new pilots when creating new air units. AFAIK there are no assigned slots for pilots, you can put them were ever you want. There are some reserved slots though, the following should be used with caution.
Ships:
Slots 0001 - 0999 Japanese
Slots 1001 - 1999 Allied
Note: there seems to be a problem with slot # 1 so I don't use it.
Air Groups: Unknown, but I use slots 0001 - 0999 for the Japanese and 1001 - 1999 for the Allies with no problems seen so far. Again there seems to be a problem with slot # 1, HQ, aircraft type and location keep reverting back to max # for that slot.
Locations:
Slots 0002 - 0099 Japanese HQs
Slots 0102 - 0199 Allied HQs
Slots 0201 - 0499 Bases & Beaches
Slots 0501 - 0999 Japanese Ground Units
Slots 1001 - 2599 Allied Ground Units
Slots 2601 - 2799 Japanese Task Forces
Slots 2801 - 2999 Allied Task Forces
Note: I recommend not moving Northern Command (slot # 109) because of restrictions placed on its ground units.
Leaders: Slots appear to be random.
Pilots: Slots appear to be random.

Hope this helps.