What I do with DP2M files is copy them from the memory card to a directory called DP2M RAWS on my working drive. I then run SPP and point it at this directory. When I see a file I want to process I double click on it to load it into the processing module.
Beforehand I also set up Preferences in SPP to save converted raw files to a specific directory on that same drive named Converted DP2M TIFFs. I set the output to 16 bit TIFF in Prophoto RBG. My preferred image processing program is Adobe Lightroom which I similarly preset with a "Watched Folder", which as you might have guessed I name Converted DP2M TIFFs. Then, whenever I press Export in SPP a 16 bit TIFF opens automatically in Lightroom ready for further processing.
As for what I do in SPP, the answer is, as little as possible. I find just about every tool in SPP inferior to those in Lightroom (or Capture One or Aperture for that matter). The only thing that really matters, and that one that one must do in SPP is white balance. I then may do some other minor adjustments, but if the file is properly exposed, I just adjust white balance and then Export the file to Lightroom.
Now, you may ask, when can we expect Adobe to support DP2M files, the way some previous X3 files have been? I can't answer the question directly, but I can tell you that responsibility for making this possible appears to absolutely lie with Sigma.