If there's time for a couple more suggestions, here are my current favourites:
1) Skyrim Creatures Alive (wilderness spawns are reworked. High level creatures are rare but possible at any level so you are genuinely taking a risk to go out wandering at low levels.
2) Realistic Lighting with Customisation - an overall weather and lighting mod with options to set the nights and dungeons super dark if you like that. Natural skies at all times of day and no performance impact from the method they use.
3) If you like hunger/thirst mods, Imp's More Complex Needs is superb. You'll need to think about your eat/drink/sleep as you go adventuring, great if you like to take your time and really get into it!
As mentioned, SkyUI is the absolute must. Your life will be a lot easier if you use the Nexus Mod Manager to install your mods.