I have never done an original research before.
I think what makes original research different from a library research is that, with a library research; the material is material from another research that was conducted by someone else. While original research would be someone else's original knowledge/material.
The library research guides original research in that it gives the researcher an idea on what to pay attention to or look at.
The pros of library research are that, the information is there for you to use as oppose to going out to look for the information yourself. On the other hand its cons are people and things change all the time. So information is always updated. But the library materials are materials that have already been done and completed. Hence might not be too current.
While with an original research the material is more current. But it could be very expensive too and time consuming.
I think the critical thinking skills involved in both types of research include observation, interpretation, analysis, evaluation, explanation and maybe inference and a little bit of Meta-cognition.
For me the most important critical thinking skill for library research is analysis. Because one has to be able to analyze the data collected to know what to use.
For an original research, interpretation and conclusion. One should be able to interpret the information gotten and make appropriate conclusions as to what to use.