1. Is it possible to create strategies with FSB pro (running on a local computer) and trade it with FST (running on a VPS)?
Yes, it's possible, but FST cannot use the specific FSB Pro features as: Indicator Signal shift, Signal repeat, Indicator symbol and Longer time frame.
2. Is there compatibility between FSB Pro, FSB and FST?
FSB Pro can load and run the strategies made with FSB and FST and offers additional features as shown above.
FSB and FST can use WTF indicators (Wider Time Frame) to imitate Longer time frame.
3. Is it possible to run two instances of FST on the same computer? (one FST is connected to demo account, the other one is connected to the live account)
You can run as many FST instances as you want.
Do I need 2 parallel installations of FST to do so?
You don't need it. FST has an option that allow using of multiple instances.
