I recommend to have at least enough NOR flash on the board to fit U-Boot in it. 256 kB would be sufficient, but you probably will not find parts below 512 kB anyway.

We use very small nor flash from SST (256kB) on our board to load u-boot. These flash also have very small sectors, so it is even possible to have redundant environment settings.

32Nand flash + 256kB SST nor flash is cheaper than 8mb nor flash from intel or AMD

Regards, martijn