number of devices usually rely on the capabilities of the
router. if you are using excitel router, it might not be powerful enough to support a large number of devices so they are probably highlighting a conservation figure. if you find that the device is not supporting enough devices, you can always consider adding a second router in access point mode in the mix and that should work. though i imagine if the IPs are assigned by the primary router, it still might cause issues.
if you have as many as 10 devices at your place, it might be worth considering asking your excitel lco to provide you with a basic onu and use a powerful router to establish pppoe connection and use it for connectivity.