do i need a third ssd for media files?

What kind of media files are we talking about? What kind of work do you do to them with Ae?

My general inclination is that a mechanical hard drive (larger and cheaper but slower) is probably better for your media files unless you can afford the higher cost and lower capacity of another SSD.

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]

[shane Scott] "im just trying to figure out if getting a SSD will speed up RAM previews or just the amount of time it takes to import the clips to AE because i cant tell if AE makes a copy of each clip when it's imported or when ram previews are being generated it ha to read information from the disk continuously from the original video file"

Ae does not copy clips. It references them wherever they are on your system.

When RAM previews are generated, Ae will read and cache data from the media files. An SSD might speed this up slightly, but it's not likely to be significant if you are doing a lot of effects work. It's much more likely that your work will be CPU-bound (meaning it can't go any faster, even with faster disks, because it is using all available CPU power).

How much RAM are you putting in this computer? What processor?

Walter Soyka
Designer & Mad Scientist at Keen Live [link]
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
@keenlive [twitter]   |   RenderBreak [blog]   |   Profile [LinkedIn]