SmartWitz syncs with your physical switchboard, your manual switches and regulators will work the same way as they used to. Switches of all brands (including two-way switches) are compatible with the Light Fan module .
Yes, any type of fan regulator is fully compatible with Smartwitz. You can use the existing regulator to set speed and also control fan speed from the Smartwitz App itself.
SmartWitz App and products are completely modular, you can add more SmartWitz modules in the App as when you buy them. You can add unlimited number of modules in one home.
This will depend on the number of appliances you need to automate. Go through the products section to understand how many appliances each product can automate.