Hello, I have experience with Open GTS, and GTSE please see past, and current work in my profile for more on this. If you plan to use Open GTS you will need a Device Communications Server (DCS) written to communicate with the device. The DCS is written in Java, I have written several of them typically it takes about a week to write, test and debug a DCS. The basic installation, configuration, and of Open GTS takes about a day. What hardware are you using, please specify the make, and model. There may already be a DCS available for your hardware.
As far as modifications to Open GTS goes, adding tabs, etc... I would need to know exactly what you require. In the end if a DCS already exists for your hardware, and your requirements are available in the commercial version GTS Enterprise, it would be far more cost effective to purchase the commercial version, and work from it to develop your project.
Regards,
John H. Ward, Jr