Hi Rohan,
I used a toroidal transformer when I built my DC power supply. Just used one transformer to power all 3 stepper drives. I can't see any reason to use one per drive.
Here's a link about toroidal transformers:
https://www.miracle.net.in/blog/adva...l-transformer/
They are supposed to be about half the size of the typical square transformer, yet are also more efficient and have less "hum". Downside is they are more expensive.
Seeing as your drives can be supplied with AC it seems all you need is the transformer. Just check with the supplier the output voltage of the transformer will be OK for continuous voltage to the drives. The data sheet says a MAX of 70 VAC but what voltage can they be supplied with continuously. Is that 70 VAC too.
Keith