I would just like to add that while you have the entire ceiling down,
if you have an attic above this room, now might be the best time to add
insulation. You don't have to take down all of the wood lathes, just
some to get the insulation in there, although there is nothing wrong
taking down all of the wood lathes either.
Also if you wanted to add some hi-hats or other light fixtures, now is
the time to do it with the ceiling down.