There are two methods of determining base traits: 1) Use the aarakocra traits from Elemental Evil, but disregard the features identified below as being specific to the aarakocra subrace; 2) alternately, use the aven base traits as-is. In either case, apply the traits of the desire sub-race to the chosen base traits. All birdfolk in the same campaign should use the same base traits. The only real differences between the two are alignment and age.
Kenku are specifically excluded from the birdfolk below. Unlike aarakocra and aven, kenku are flightless--a feature core to the lore of the race. Kenku should be treated as a unique race, related to other birdfolk as gnomes are [often] related to dwarves.
Concerning Arms & Other Human-like Traits
The birdfolk of Monvesia, called tengu, are four-limbed with bird faces like older-edition aarakocra and the aven of Tarkir. The known sub-races of this setting are marked with an asterisk (*), below.
These are also the dominant aven race of Dominaria.
In Monvesia, they are called garuda (Henjali) or karura (Fuhongo).
These are the hawk-headed aven of Amonkhet, the aven from Bant on Alara, or the Temur and some Jeskai aven of Tarkir. They are also the Horakhtites of Nefret.
These are the ibis-headed Aven of Amonkhet, or some Jeskai aven of Tarkir. They are also the Jehutites of Nefret.
These are the aven from Grixis on Alara, or the Abzan aven of Tarkir. They are also the Nekhbites of Nefret.
These are the peaceful aven of Dominaria.
This subrace is based on the aarakocra description from Elemental Evil, which mentions aarakockra that resemble parrots.