You need a mobile phone since they don't have internet access directly.
After that you should be totally fine, what are you hoping for your smartwatch to do? I primarily use my pebble for notifications from my phone to show up on my watch which doesn't require any sort of external access.
I need it to track my heart rate. I am actually also looking forward to something that can track my blood-pressure, but I am not sure whether the technology is there yet. A device that can do offline tracking would be ideal, ability to sync with a USB cable would be icing on the cake.
After that you should be totally fine, what are you hoping for your smartwatch to do? I primarily use my pebble for notifications from my phone to show up on my watch which doesn't require any sort of external access.