I was looking for an earlier topic on these forums that might be of help, and I then I saw you were the original poster on the topic.... so you probably saw http://www.gamesas.com/index.php?/topic/1150909-importing-models-and-textures/ already. Just look at what Ghogiel wrote towards the bottom about setting up the ##SightingNode.
I haven't tried it myself yet, but it seems easy enough. From what I can tell, all you need to do is create the node in Nifskope and then position it as desired.
Although I don't really understand how you can ensure that the position of the node will result in an "accurate" sighting system for the weapon. Perhaps it just comes down to trial and error... keep positioning the node in Nifskope until it looks right in game.
As far as I know, the ##SightingNode is not actually required in order to use weapons in FONV. Without it, the weapon will function like FO3 I think... by zooming in on the HUD reticule. Also, I don't think scoped weapons need a ##SightingNode because they don't use iron sights obviously.
As for what settings to use with the weapons in the GECK... that will vary greatly depending on what you want the weapons to do... ultimately its a matter of personal preference. I've found http://geck.gamesas.com/index.php/Weapons to be helpful in setting up GECK weapons, but its for the FO3 GECK(not FONV). I'm sure some of the settings are the same in both games. Its also very helpful to look at the settings of a similar weapon already in the game and then use those settings as a starting point for a new weapon. I typically clone a stock weapon from the game first, and then switch the models and change the various stats as desired from there.