I would strongly encourage you to NOT use Sessions and, instead, just import your images that you want to work on in C1 7 into a C1 7 Catalog that you sort of run side by side with your Lightroom Catalog. Be sure to check the box that allows you to leave the files in their original locations. I use LR 5 as my primary catalog/ asset manager and use C1 as an alternative raw processor for certain files where it does a better job than LR. This is not ideal in some ways, as you really need to move files around only in LR if you want to maintain the integrity of the LR Catalog. After I work on a file in C1 7 and I am ready to process it, I export a 16 bit TIFF to the same folder as the original raw and with a file name that indicates it was converted in C1. I then have to remember to import that 16 bit TIFF into my LR Catalog.
With Sessions, C1 dictates your file organization, not you. It's an anachronisitic vestige of C1's original role as a software tool for tethered capture for Phase digital backs.
Yes but beware of Catalogs in C1 if you want to port from one machine to another - laptop to desktop for instance. If the files in the Catalog are 'referenced' i.e. left in the original location and not imported into the catalog then the catalog won't work on the second machine. If you import the images into a Session or a Catalog then it's simple to transfer either to another machine.
I'm not sure I understand the comment that C1 dictates your file organisation. Perhaps I've missed the point but I don't find C1's file organisation to be a constraint. Exporting as a TIFF from C1 and then importing in LR makes sense if that's what you want to do.
You can also import LR catalogs into C1 though I haven't needed to try this.
Six of one and half a dozen of another but I have found you lose portability between machines if you reference files in their existing locations rather than importing them into a Session or Catalog.