I have an iPod and iPad which I sync with my Mac. My wife has has an iPod, iPhone and iPad which she syncs with her Mac.
These are all associated with the same Apple ID.
I am planning to buy an iPhone, basically to replace my iPod.
I understand there is a limit to the number of devices, although I have not been able to discover the devices associated with my Apple ID.
http://support.apple.com/en-au/ht4627 has instructions which I have followed.
There are 3 computer authorisations listed, but there seems to be no Manage Devices
on the Account Information screen
.
NOTE We do not use automatic downloads or iTunes Match. I am only interested in apps