For my 4' x 8' table I'm planing to use Nema 34 motors with around 12Nm for the x and y axis. Is it overkill to use the same for the Z axis (planing for any future upgrades) or should i go for a nema 23 with around 4Nm?

The motors will be driven by rack and pinion.

What would be the best digital stepper drivers, breakout board and power supplies?