So I've played a good number of hours in daggerfall, morrowind, and skyrim. Never touched oblivion though. What mods would I need to enjoy the gog version of oblivion?

Got a pretty good pc with a gtx1080 so graphics mods are also welcome in addition to gameplay ones.

The most important:
http://www.nexusmods.com/oblivion/mods/5296/
http://www.nexusmods.com/oblivion/mods/10739/

Just these two and I'll be good?

Oblivion is pretty good vanilla; you don't need much. The one thing that's bad about vanilla is the (IMO) terrible level scaling. I always used either OOO or Francesco's for that reason but both of those mods make lots of changes.

Pretty much... i personally suggest also Darnified UI, which is a much more pleasant and functional interface, but other than that, the patches are all you really need for a smooth first playthrough

You can then go mod-crazy when you replay the game, there are tons out there that will give you a substancially new experience

I'm obviously going to suggest my guide on this subject.

What is an essential mod really depends on every one and if this is your frist play or not. I personally cannot play Oblivion without a mod like Oscuro's Oblivion Overhaul that fixes the dumb loot and NPC scaling, I find that even more essential than any texture mod although I agree that for a first time play you don't want to change the gameplay so you're looking at graphics/sounds/UI/convenience mods. My guide is designed to mix and match, describes every mod covered and provides a "recommendation level" for each.

Wow, good guide. I'll try it if I ever get around to another OB playthrough. Kind of stuck on Morrowind lately.

Slightly off-topic: What do you recommend for running a total conversion like Nehrim in addition to Oblivion? Nehrim points to the original Oblivion folder in addition to copying files from there. I have no problem running Oblivion and Nehrim as long as only one of them is installed.
I once installed Oblivion with the Unofficial patches, then Nehrim, then copied the Oblivion folder and installed the Oblivion mods I'm using (mainly OOO) to that new folder. I also installed Wrye Bash for Oblivion and Nehrim, but not OBSE. In the end, the whole thing didn't work anymore, either because I made a mistake or because one of the programs involved got confused (as far as I can say, it had nothing to do with the ini file(s)).
Is there a specific way / sequence to set such a configuration up that it works in the end? Have you ever tried to install Nehrim after OOO was installed for Oblivion, and do you know how OOO impacts the balancing of Nehrim (if Nehrim with OOO works at all)?

Sorry, I have 0 experience with Nehrim. Never installed it or tried modding it. I only have this vague memory that one of the grass mods I was trying had a Nehrim ESP file.

If Nehrim references assets form the original Oblivion Data directory it might work to install texture mods for Oblivion that may be picked up by Nehrim and although those won't crash your game I think it's likely they will not match Nehrim's own textures, ie you cannot just take a few random meshes and textures from a pack like QTP3 and expect those to match (visually) with vanilla or Nehrim meshes and textures as these packs are designed to change a lot of things together.

Don't forget the DLC unofficial patches.

Has anybody who recommends these unofficial patches gone 10 levels without a crash?
I can without the patch, but with the unofficial patch installed, I can't go a hour without a random crash.
I got the GOG version because I thought it might have been my disk version needing a different official 1.2.0416 patch than the mod was made for, but the result is the same, hours without a crash when not using the unofficial patches, random crash in < hour with it.

I didn't use DLC unofficial patches. My game didn't like it and was crashing (hence I didn't add it to recommendation list). However, normal unofficial patch and Shivering Isles unofficial patch behave normally for me.

Yes. I had a crash once after some hours of playing, but I blame OOO (strangely enough, game runs much smoother without it). Version of my game: 1.2.0416. I didn't patch it up with new GOG patch, because I feel lazy.

I play with all the mods listed here and can play for hours without crashes. That list includes UOP, UOP SI and DLC UOP. I am currently level 12.

If you get recurrent crashes (ie happens around the same interval of game time), open Task Manager and monitor Oblivion process memory use. If, while playing, you see it steadily growing and then when it gets around 1.8G it crashes, then you are hitting a known memory leak bug in Oblivion (but usually that leak is only an issue when heavily modding the game as the vanilla game consumes memory at a much lower rate, allowing the game to be played for many hours before crashing). The fix for that particular issue is a combination of OSR (Oblivion Stutter Remover) heap replacement function and ENBoost. Both are documented in the link above.

Another potential cause for problems is bad installation of those mods. After installing the mods have you run BOSS to order them?

If you still get crashes after using BOSS and it's not happening when Oblivion.exe reaches ~1.8G of memory it's possible you have a corrupted savegame. This is something that can happen with Oblivion if you use quicksave a lot (ie if you overwrite the same savegames often, sometimes it corrupts them, which is why in my guide above I recommend always saving to a new slot). The following procedure may be able to clean up your savegame (it's usually used when disabling mods from an existing savegame, but maybe it's going to help you too):
1. Load savegame, wait 5 seconds, bring in the console (type ~), then type "coc testinghall". It will teleport you to a special testing location, make a savegame in a new slot, quit the game
2. Start game, load the testing hall savegame, wait 5 seconds, use the ingame wait function to pass 72 hours ingame, save game to new slot, exit game
3. Start game, load the latest save game, wait 5 seconds, type "coc weye" in the console, it will teleport you to a house in Weye (the village near the imperial city bridge), make another separate save, quit game

Now you should have a clean(er) savegame that hopefully will result in fewer crashes. Try to avoid overwriting savegames in the future :) (I'm actually currently testing a small mod that makes it easy to do this by automatically saving to a new slot every time you press F5 so that you don't have to go through menus every time you need to make a save).