This is one of those times when you start small by hand with a test in an inconspicuous area and use the test results to continue. I'm betting you'll go by hand; the power hammers are just too destructive to the substrate fabric.

I did this once to a chimney running up through a back bedroom in a home from the 1870s-1880s. It was originally used for stoves in the bedroom and kitchen below. Just plaster on the brick. However, once exposed, the brick was ugly and I painted it instead. The plaster was likely original and the brick was chosen for utility, not appearance. Be prepared!

a few years ago I was recruited to help someone
remove plaster off brick in a historical bldg.

we started with chisels & hammer.
slow going..sore hands.
tried different tools...but architect was worried
about damage to brick.

so we wound up chiseling off the plaster.
huge pita. but looked great once it was
finally done.

btw...I wouldn't do it again for the same $$
price would be 5x because of the slowness
of the removal.

if you hire it out...don't pay by hour...LOL!

best of luck.