Could additional mods be added to improve the experience?
How about Will-o'-the-Wisps? Seems to fit the theme, the wisps come out at night -- although I'm not sure whether that's based on time or darkness.
Can mod settings be changed for a better overall feel?
I take that as a technical question, see "Recommended Settings: (Because I can't figure out how to set all of them through this pack)" on the info page. Yes you can change the settings of other mods, in settings-updates.lua. You'll have to get a list of the setting names and types (look in each mod's settings.lua) in order to pull that off. There's a nice mod-settings tutorial on the Wiki. You definitely should read it from the start (I've found something new in it right now), but the part that's probably of most interest to you is the section Changing another mod's settings.