Yes, currently we do not have a device simulator, so you need to have a device or have access to an account with a device attached to use the API.
No, the API calls and commands back and forth from the device require an internet connection.
Our limit is designed to allow you to poll device status every 5 minutes for up to 20 devices per hour, with a little cushion to make changes. If you need a higher rate limit, please contact us: HoneywellAPISupport@honeywell.com
Absolutely, we sell a number of other highly rated Wi-Fi thermostats. We have an API for that too, but the information is not yet public. For more info please contact: firstname.lastname@example.org