Absolutely. The node trees have been set up in a way to make it very simple to navigate and input new information without the need for creating new nodes - unless you're looking to change the material type. Simply input the new RGB values and navigate to the appropriate section where you'd want to intensify or diminish certain effects to get personalized results. From there you can save it as a brand new material (Pro version only, of course)

To a degree. There are many workarounds one can employ to achieve a similar result you'd find using the Cycles renderer, but they ultimately perform best using Cycles.

Yes, it does. There are no limitations or differences in performance in either version (FREE or Pro)