I would probably go with something based off of the F-keys, for targeting your team.
That is the default settings.
And you can invite in a fixed order if you want.

The 1, 2, 3, 4 etc DPS keys, will be for DPS in every vehicle you use.
But you could as easily map the keys to A, B, C and D.

In the end, it doesn't matter which way you go, as long as you know your system.