simple switch for mains power
Your switch is likely suitable for your project. You provided the specifications for the switch, but you omitted the specifications for your load (your active speakers). 

Yes, it is perfectly acceptable to switch only the hot/live side of the power mains and leave the cold/neutral connected.  Of course, you must remember to also include suitable wiring for the green-wire safety ground.

However, you said "i don't know much about electronics.." and this is a project that involves power mains wiring.  It is rather an ambitious project for your level of experience.  It would seem much simpler to use something readily available like a simple power strip.