All eTap AXS components are compatible with one another, the compatibility chart is super easy. (Note that AXS implies you have a 12 speed drivetrain, you can’t match older 11-speed Red eTap shifters with 12-speed front and rear derailleurs.)
I think the best bang for the buck is a Rival eTap AXS groupset with a Red crank.
Parts availability is a nightmare.
I had to wait 4.5 months until my bike was delivered and assembled. And I had to jump through some hoops (e. g. my bike shop organized a RTP frame at no extra cost and had it painted for a modest amount). And I forwent Red cranks, because those would have needed another 2+ months. I didn’t want to wait until June or July for a bike I ordered in January.