Well, here's my "4-stage plan" which would IMO bring AH planeset "close to completion" in as far as special events and historical significance goes. I haven't listed any variants of the existing planes (LaGG-3 and C.200 could be argued but they'd still take significant changes to the exiting models to make them), just totally new airframes...
The numbers indicate the order they would be added.
1.
Ki-43
Pe-2FT
Yak-1b
LaGG-3
G4M2
2.
B6N
D4Y2
He-111
SM.79
Wellington B.Mk III
3.
C.200
Hawk75A
Beaufighter Mk.X
Il-4
Ki-21-IIa
4.
CR.42
I-153
Ju-188
Ki-44
Me 410