Hi Vivek,
1. Once you have your ECC box with an integrated ITS, you will not require any licenses.
2. This can be extended to android / iOs tablets. The only downside is you will need to create ITS HTML pages for each device that you employ. For example, if you use android tabs only, you will need to create ITS HTML templates for all the screens in your application only once to suit the dimensions of tablets. If you employ more devices, you will need to create additional screens to adjust to those new dimensions (pixel sizes).
3. Majority wise, RF guns are used for employing this solution since it has an RF scanner.