How can I isolate my guitar effect circuit from outside noises & interferences?
Can I have effect's enclosure used as a shield like Faraday cage?
Do I need to connect circuit's GND to enclosure or the floating GND (like in attached circuit)?
It all depends on how the noise is entering the circuit. If it's electromagnetic, yes a shield will help. If it's coming in the power supply or signal leads, shielding won't help.
If you have electromagnetic noise in the area, you need a metal box to enclose the circuit, filters on all inputs and outputs, and ground the box at one point, inside and outside.
