1) I've got several macros on some screens, so that doesn't seem correct.

2) The Take Control doesn't actually have source switching commands attached to each device/activity. This must be done through a macro, which you can replace the activity shortcut on the home menu with, but once you've done that there isn't any way to NOT send the macro to select the device (unless you have duplicates).

3) Not yet. It doesn't give you "free memory" status, but there seems to be enough. There are limits on the number of devices/macros you can have; I believe it's 16 and 32 respectively.