Imho 4mH is not *that* high inductance, and it certainly does not look like a high inductance motor type. So imho you could just buy a 24v power supply from ebay or use a 12v atx one.
The 3.5A per phase in case of 2 phases goes to double because the driver feeds both coils at same time, maybe in opposite directions, but still "at same time" (not intermittently). But that 3.5A is max current, you dont have to hit the max because thats what "max" word means, just stay below that. However you would still need a serious stepper driver unit for it if you want full power because the mechanical power delivered by the motor depends solely on the current level, which again depends only on the driver (presuming psu can deliver). But how much power/torque you really need, that depends on your application. Hard to say from verbal descrition but to manipulate a sample holder probably a nema17 motor could be enough.
The 3.5A per phase in case of 2 phases goes to double because the driver feeds both coils at same time, maybe in opposite directions, but still "at same time" (not intermittently). But that 3.5A is max current, you dont have to hit the max because thats what "max" word means, just stay below that. However you would still need a serious stepper driver unit for it if you want full power because the mechanical power delivered by the motor depends solely on the current level, which again depends only on the driver (presuming psu can deliver). But how much power/torque you really need, that depends on your application. Hard to say from verbal descrition but to manipulate a sample holder probably a nema17 motor could be enough.
