Peter, You need to figure out the motor specs before you do anything about drivers. I've seen Nema23 with nominal current from 0.4A all the way up to 6A.
In case if you don't have specs for the motor, you can measure the resistance and then based on the resistance and size of the motor, try to find something similar on stepperonline site.
Most people use Nema 17 for your mount, something like this:
https://www.amazon.com/gp/product/B00PNEQMLY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1