There are setups out there that use sequential throttle plates. I'm not sure if GM does it. there's typically a smaller throttle plate and then a linkage to a larger throttle plate. When you crack a single large throttle plate, the open cross sectional area jumps pretty quickly which can make driveability an issue. GM specifically dealt with this either by using multiple smaller diameter throttle plates or by using a half shell on one side of the throttle plate so that only one side of the butterfly cracks initially. I'm probably not describing this well, but look up the stock throttle on the Vortec GMT400 trucks and you'll see the lip on the throttle plate. That's what that plate is for.
All of this is to smooth out throttle tip-in and light throttle behavior while still allowing a lot of airflow at WOT. Modern electronic throttles have rendered this unnecessary.
You don't need multiple staged injectors to do what you're saying. You would use a mechanical linkage between two plates, and the TPS would be on the cam that the throttle cable controls, not on either of the plate shafts themselves. The MAP or MAF sensor would read total airflow or vacuum, it doesn't care how the throttle is set up. Tuning of your injection events would be the same process as any other setup.
The reason people use staged injectors is because massive oversize injectors have poor resolution at small pulse widths. So a set of smaller injectors for light load and a set of larger ones for high boost, fuel types that require high volumes, etc. The engine setup you describe isn't wild enough to need such a setup, even good size 38-42 lb/hr injectors will do idle and low load just fine and will be more fuel than you need if you're running a set of 8 multi point. TBI would be a different story, but if you're going to all this trouble to do a staged throttle setup, TBI style injectors shouldn't be on your radar anyway.