Grab the unofficial patches for any dlc you own as well as skyrim.
Grab skyUI
Don't forget skse as it allows you to run script mods.
Immersive armors has a ton of both gender lore friendly armors that really add to the game.
There's a mod to give those armors to certain npcs as well called immersive armors for npcs.
One mod I highly recommend is Skyrim Redone bt T3nd0. He re balances everything giving every perk tree plenty of use and viability.
Frostfall will give you a weather based survivalist mod where cold areas can cause you to freeze if not wearing furs.
I highly recommend realistic lighting overhaul and it's weather mod as well.
Look up better males for a really good male body, it's nude but has a non nude option.
Unp or cbbe are the best female body mods. I suggest Unp as it has two mods with armor chopped into modulated parts making it easy to get the look you want.
Look up broke fist for a mashup and Hmmm what to wear for another. Both are Unp only.
Grab the x32 skeleton, has the ability to place weapons in the back and can be used with realistic ragdolls and force. Just don't ever overwrite the skeleton, it's compatible with every mod that requires a modded Skeleton. Dual sheath redux I suggest as well. Install both of these mods before animations.
You will want some new animations, I recommend getting these and installing in this order:
Realistic running sprinting and jumping
Immersive animations
Mystic knight animations
Choose what ones you want from each.
Check out the skyrim monster mod, adds new monsters to the vanilla spawn points. There's an immersive version that is lore friendly.
Sky tweak serves as a management tool for all of skyrims values like dialog padding (time delay between voice lines), fall damage, magical costs and many many others.
Back on skyrim redone or skyre, I suggest this because it does a lot of changes without having to download several mods that might not be compatible to get the same effects. Races all have unique and fun abilities instead of the boring vanilla ones. It's a quality mod.
Dance of death allows you to use all kill moves regardless of weapon and alter the kill move chance.
Heart breaker allows to to rip out the hearts of enemies on a knee, good for playing a conjure mage with skyrim redone.
Location all damage gives you incentive to play combat tactically by giving each body part a hitbox, and a negative effect or two for hitting it. Throats cause bleed out till death, head shots deal more damage and arrows can be a one hit kill. Groin causes a short paralysis, leg hits from behind knock down, it's just like a more realistic approach to combat. Also hitting arms will reduce weapon skills.
Grab ultimate combat, tk dodge, dual wield parry and animations for it, and enhanced enemy ai. This will make combat very challenging. Unlike spamming in vanilla, attacks should be used with caution as they leave you open. Enemies will use tactics s similar to wolves in they will surround and pounce when your attention is diverted.
Since skyrim is now a difficult place you will want a follower tweak mod, I suggest AFT its script less and noninstrisive. Adds options for your followers and the ability to have many more
Skyrim flora overhaul with goldielocks grass on steroids and bigger trees mod. This makes skyrim feel like it's supposed to.
All that's left really is to grab some mods you like. I like to change the speeds of everyone so walking is worthwhile, running is a light jog and sprinting is a run. I then use unlimited sprint to counter my slowness.
When I get off work I can check my mods and list some more that I feel are essential to an immersive play through. Nothing more fun that getting lost in a TES game feeling like you're the character.