I did a few sides of salmon over the holidays using a pretty similar method. I decided to "Southernize" my version up and used a little bit of rye or bourbon in the cure and then cold smoke with pecan and/or apple wood. The only spice I put on was black pepper.
I went off my recollection of making gravlax many years ago and cured for 48 hours. No ill effects in terms of saltiness. Weighting down the filet to cure makes it denser, I think. I watched a video online (
http://foodcurated.com/2010/04/samaki-smokehouse-the-art-of-cold-smoked-salmon/) where they brined the filets. I suspect that preserves a softer texture in the finished product.