SPI Vs i2c does not matter in your project. Both are way faster than any motor.
If you use 74hc595, mcp23008, mcp32017, mcp23s17, pcf8574, pcf8575, then you will need one of those uln2003 driver boards for every motor.
If you use tpic6b595, you won't need the Uln drivers. This could save you a lot of clutter and wiring and if you can buy the motors without the Uln boards, save money and reduce waste.
Not sure about A4988. It is a bipolar driver and 28BYJ is a unipolar motor. It may be possible to wire 28BYJ for a bipolar driver. But you would need a A4988 for every motor, and also shift registers to drive the A4988s, so lots of extra expense and complexity for little benefit I suspect.