What basic/essential mods should I install?

[Juugo]

I've never played Oblivion before only Skyrim.

[Horror Pigeon]

Focus on performance and crash fixes

[I'm the walrus]

no mod needed just look up ini changes at best and download body type to male/female mod if that angers you .

[The Minted Lady]

I found some on Nexus that will highlight books you haven't read yet. That one sounds very essential to me. I had a similar mod for Skyrim to help me make sure I was getting all the skill books.

[ZemX]

I wouldn't get too deep in modding just yet. There are likely to be one or two patches here before too long and they will break a lot of mods until the mod authors update. At least the ones that rely on script extenders, usually.

Ones that just modify resources like models, textures, and item/NPC lists are usually okay. I am using the Ascension-Lite plugins for loot and creature levels. And one for balanced de-leveled rewards.

[Twelve]

I'd recommend Ascension Remastered and the accompanying mods the dev has made. Just because it fixes a lot of core issues the game has around level scaling and enemies having nonsensical equipment

[PocketYoda]

I haven't added any the game seems fine without them.