Scalability with Node

Hi,

My project has 5,00,000 multimedia media files.

What I need to know is,

(1) 500,000 multimedia files on website means 500,000 nodes or not?
(2) Whether all these nodes will be loaded always, or loaded only when they are accessed by someone and release when user moves out of that object.
(3) What performance degradation can be caused by high number of such objects
(4) is there a better way to architect this?

I'm waiting for your solution for the above issues.

Thanks & Regards,
Karthikeyan