Can someone walk me through the steps I need to take to completely
detile my shower and remove the drywall behind it?

We don't need to worry about saving the tiles, drywall or shower pan,
all are being replaced by a professional tilesetter.

But we want to do the demo work ourselves to save money. I know we need
to get down to studs and, as I understand it, the subfloor beneath the
current shower pan, which was probably built 20 years ago.

I suppose the easy answer is to just take a hammer and prybar and start
to work, but I've learned that easy answers aren't always the right
ones in home repair.
I want to make sure we don't damage the plumbing, and I don't have any
idea at all about how I should go about removing the floor tiles, which
are set pretty solidly into whatever was used beneath them.

Thanks so much!