I see no reason that a triangulated four link wouldn't work, provided the geometric and mounting point requirements are met. The old Ford "wishbone" suspension is a good example of triangulated suspension! You should consider a track locator or panhard bar unless your angles can produce a sufficient lateral stabilization effect.
The airbags are just like any other "spring" apparatus. A coil, a transverse leaf, a torsion bar, quarter elliptical, or regular longitudinal leaf setup do nothing more than hold up the vehicle, (the load). The spring rate and the location of the spring device in your suspension will determine hight and rebound. The shock absorber controls the speed of the compression and rebound of the spring device.
As to the rack being mounted to the axle. It can and has been done. You'll have to allow for changes in position through all three planes of motion at the same time!! As the axle moves when traveling, it moves up and down AND forward and back!! It also "yaws" when one wheel rises or drops in relationship to the wheel on the opposite side. Add to that the fact that the axle also rotates slightly as the vehicle rises and falls!! The steering shaft will need to freely and safely telescope and NOT bind when these other motions are transmitted to the shaft. When one side or the other of the axle changes height, it will influence the steering as the rack pivots around the pinion, creating some level of "bump steer"!! ALL steering systems have some amount of bump steer. How much is acceptable and safe is the question to be answered!! Keep all these things in mind and remember that you'll have to provide for each of them 'cause it'll directly effect how the car drives!
Hope this helps!! Ask any questions and show us pics!! We're all glad to help!!