I would suggest trying a small (Hilti TE-54 or smaller) variable speed electric hammer
(one that has rotary hammer & hammer only settings)

NEW TOYS!!! :O) I think I can snag one of those. I do have a
decent compressor, would a pneumatic hammer be cheaper?

in hammer only mode with a flat wide (2" to 4") chisel blade. Use "little hammer" setting & gently chisel under rocks at a very flat angle. They should pop right off & you should be able to get rid of the majority of the cement / mortar that adheres them. *Finish off with angle grinder & a cupped diamond disc.

Already got the grinder. I had one pop/fall/get kicked off already.
But the back concrete looked solid.

Mortar / cement has relativley low bond / tensile strength so "wedging it off" will work.

I have a lamp post by the front door that's block and about 18" square
and has the stone on it. We're replacing that and my GF suggested we
use that as a test area but I wanted to ask around first. Didn't
want to just get in there and start hammering away.

If the block is sound you should be able to remove the rock with virtually no damage to the block.

Sounds good. Would like to give the whole house a new look. And
getting rid of the stone allows us to do siding all the way around.

If the stone was set with metal ties you'll have to be a little more careful but it will still be doable. *Use a 4.5" angle to attack the ties as they become accessible.

Don't think this is an issue but I can check.

How many sq ft?

Not sure exactly but both sides of the garage door have it, probably 3-
feet wide and 8-feet tall and then wrap around the edges about a
foot. Then there is a wall section to the left of a bedroom window in
the front that has it, probably 10-feet wide and 8-feet tall and wraps
around the corner about a foot. Deed restrictions were that front of
homes needed to be brick, stone or wood. So this stone trim has rough
lumber siding between the stone sections but the sides and rear of the
house are painted stucco. Not sure if we want to undertake removing
all the stucco.

Can you put siding over top of stuccoed walls if the stucco was ground
pretty flat?