Hardrive space means absolutely nothing when it comes to ingame performance as these mods will kill Frames per Second which are CPU and GPU dependent.
http://www.nexusmods.com/skyrim/mods/607/ - 2k Textures
Increases Detail on all textures by several times.
http://www.nexusmods.com/skyrim/mods/1111/ - Pure Waters
Makes Water much better looking and more realistic.
http://www.nexusmods.com/skyrim/mods/17802/ - CoT, Adds over 2000 unique days and Nights to the Game with overhauled lighting visuals and a new weather system.
http://www.nexusmods.com/skyrim/mods/8655/ - SMIM - Highly Detailed Mesh Replacements of many in game Objects but Heavily Increases In game Polygons and can slow the in game Performance down by quite a bit.
http://www.nexusmods.com/skyrim/mods/52322 - Windsong Character Overhaul, Chaarcter Model and Appearance mod that adds a variety of Character Models to choose from including CBBE and UNP alongside Better Males as well ans facial mods. (WARNING May Contain Nudity)
get these as well as they fix thousands of ingame bugs -
http://www.nexusmods.com/skyrim/mods/19
Unofficial Skyrim Patch.
http://www.nexusmods.com/skyrim/mods/23491/
Unofficial Dawnguard Patch.
http://www.nexusmods.com/skyrim/mods/25127/
Unofficial Hearthfire Patch
http://www.nexusmods.com/skyrim/mods/31083/
Unofficial Dragonborn Patch
Only get the patches for any DLC you may own regardless of what you have definitely get the Skyrim unofficial Patch
Now you say your just Picked it up so is this your first time ever playing Skyrim? well after a time if you want to make Skyrim More Immersive and Realistic May I recommend these mods as well
http://www.nexusmods.com/skyrim/mods/11163 - Camping and Hypothermia survival mod, Forces you to act safely in Bad weather Conditions and dress warmly when in locations that would kill you for being so cold in real life.
http://www.nexusmods.com/skyrim/mods/26228 - Realistic Needs and Diseases, Forces you to Eat food and Drink liquids during your adventures or else you can die, it also makes disease you can catch much worse
Now if you want recommendations for Vampire, Werewolf, Weapon, Armor, Player Home or Quest Mods just ask and I shall Provide the Links to you.