I just had a quick question about IA interacting with r4-d6. Let’s say Biggs has 2 hull left, but receives an attack with three hits and no evades. Could he use r4-d6 to take a stress and receive 2 hits, then discard IA to take it down to one hit?

Yes, IA and R4-D6 work as described.

Let's see: R4-D6 allow you to take stress instead of suffering some level of damage. IA allows you to discard your Astromech to discard an incoming damage card without effect. With an attack you aren't going to have an incoming damage card until after you've suffered damage so the order it pretty clear.