Could I substitute paneer for chicken to make butter paneer? If so, would I want to use an equivalent weight or go by volume?

Yes you can substitute and go by volume. The masala gravy is adaptable to other ingredients (chicken, vegetables, etc) so you don't need to stick to the recipe to the exact "T." I'd probably adjust the cooking time if you're changing the main ingredient and as always, experiment with a smaller quantity in the first go-around before moving on to bigger batches!

Yes - I have done that plenty of times. Would suggest by volume than weight.