Decide exactly which music sources (CD, AM/FM tuner, DAB, etc) you want to listen to and where you want to listen to them.
Unless you’re on a really tight budget go for a wired setup rather than wireless setup. It might be more messy and expensive in the short term but it will be more flexible and reliable.
If you live in a lease/rental property, don’t forget to ask the permission of your freeholder if you are planning to get in-wall or in-ceiling speakers installed.
If necessary get the speakers sprayed to match your decor so they are as discreet as possible.
Check that you are not likely to invalidate your buildings insurance if you install speakers in a party wall.
Visit demonstration rooms to get some idea of how the ceiling speakers may sound before installation. Be prepared for sound to vary according to where they are placed, construction of the wall, etc.
Work with custom installers to make sure that any keypads provided meet your requirements. After all there is no point having a state-of-the-art multiroom audio setup if you don’t know how to use it.