post processing - Please suggest a workflow on Mac using only free/open source software

I own a D90 with a Nikon 50mm f/1.8 prime lens. However ever since buying my camera I am struggling to find a proper workflow to process RAW images on my Mac which does at least the following

1. Adjust shadows and highlights.


2. Adjust an image via its histogram.


3. Adjust white balance.



4. Adjust exposure.


5. Crop a photo.


6. Present a preview of how the photo may look like after printing.


7. Apply EXIF tags.


8. Apply watermarks.

So my question is what kind of workflow should I follow, if I were constrained to use only free software on my Mac?

Edit: Please also suggest a software or a set of software applications to use.

Edit: Flagged as a wiki question since there can't be correct or perfect answer.

Edit: Given the fact that a freeware will probably not be able to cut it, I have come to the conclusion that I will need to buy a low cost software for this. I am keen on using Lightroom but may have to settle with iPhoto.

Answer

Given that the reason for the question is price, I encourage you to rethink this constraint. How much is your time worth? You can get excellent post-processing software for little money compared to a lens. For example, Bibble can do everything above in the same application (might need a plugin for the watermark) and it costs only $100 for the lite version.

I tried to go the same route (on Linux) and got tired of screwing around with freeware. The commercial software is way better and your time is worth more than you think it is - particularly since the smoother post-processing is, the more fun photography will be. :)