Hi
I am a VT Builder developer and will try to answer your questions.
If i only use krpano to build website, will i must purchase krpano's license key (for approximately $200) and VTBuilder plugin ( for approximately $130) separately or just purchase the krpano's licence key that contains all plugin ?
Yes, you need your own Krpano licence.
Except VTBuilder, can you recommend me some other plugins that have the same function ?
I recommend checking out VT Builder's little brother,
the CMS4VR system .
regards
Piotr