For a project I have, there is 1x arduino, a transistor that needs 9v, and a relay with 110v AC. I have plenty of 12v power supplies from external hard drives and the like. This also has the benefit of being easily chained to the 110v AC in the same project box.
It looks easy enough to drop 12v to 9v (7806), and easy enough to drop 9v to 5v (7805). Should I be fine taking a line from my 9v into the regulation for my 5v, or is having multiple regulators and down steps in a chain a bad idea for any reason?