For Graphics, use Realvision ENB, most easy to install.
There are plenty of high res overhauls. Checkout the Nexus for that.
I use "live another life", from Arthmoor. And probably all his other mods, including Open Cities.
Open Cities lets you walk in and out the city without the loading screens. Battles can continue and it is much more immersive.
There are mods that alter the main storyline or even remove the dragon part. Never tried those, as i'm a natural Dragonborn
But in the best playthroughs, like my current one, i completely ignored the civil war and only did some part of the Dragon story. If you just leave Alduin on the throat of the World, the story simply stops. Besides the occasional dragon attacks. Don't learn the Dragonrend shout
There are some mods that intensify or overhaul certain factions, like the companions or thieves guild. And change the way sneaking or other "skills" work, so it becomes a lot more immersive to play.
Best is to take some time and browse the Nexus. User rating might give a good idea if something works right
I run about 250 mods now and use ASIS and a savegame cleaner to get rid of conflicts.
SkyUI and SKSE are needed to enable larger scripts and have in game control of mods.
Use LOOT to set them all in the right sequence.
Nexus MOD manager has evolved a lot.
There are mods that use HDT physics extentions. From facial expressions to hair, capes and boobies.
USLEEP is the community mod that fixes most bugs. But it is for legendary edition only now. All DLC.
To get better distant scenery, you can use DynDoLOD. It makes custom LODs based on your installed mods.
And off course the increase to a 7x7 grid in the INI. Larger will trigger events too soon®
Simply too much to point out in a single post.