Apologize if this is a noob question, but do custom Papyrus scripts need to be packaged and included with your mod for others to download? I've seen them in a couple of mods, but not in others, although I am not sure if for those times where they were missing they were actually compressed into a BSA file.
Yes they do. Papyrus scripts aren't included in the plugin like they were in previous games so you'll have to package the compiled scripts with the rest of the mod. I believe that they can also be added into the BSA file (but I'm not positive on that one).
You must include all loose files that your mod uses that aren't part of the vanilla game. (I.e. anything you create specifically for your mod, like scripts, textures, meshes, video's, voice acting, etc)
You have to include the *.pex files (pack them into the bsa using the Creation Kit) The *.psc files aren't needed for the game to work, it's like the source code - you choose whether you want people to be able to check how your mod works.