Can someone list the difficulty levels and explain how they are different? Is there a hardcoe mode?

There's no hardcoe mode. AFAIK we don't know how difficulty scaling works (in past games you'd do less damage to mobs and they'd do more damage to you with each increase in the difficulty setting). What we do know is that the Survival mode makes it more likely for legendary enemies to spawn which are more difficult to take down but they also have better loot.

harder enemies also means you need more bullets so youre more out of ammo and need more money

I would much prefer it if only their damage against you where increased, don't want to have to shoot a non armored humanoid 5 times in the head for them to die, regardless of difficulty settings.

Yep.. make me weaker. Keep the enemies the same. That's how it should be. Probably won't be.

I'm guessing they will give them heavy armor so it wouldn't be unrealistic to shoot them more. With creatures maybe they have a thicker skin? If they are unarmed and it takes 5 headshots it is dumb though I agree!

Just a guess, but:

Very Easy: -50% enemy damage, +100% player damage

Easy: -25% enemy damage, +50% player damage

Normal: Baseline

Hard: +50% enemy damage, -25% player damage

Very Hard: +100% enemy damage, -50% player damage

Survival: +150% enemy damage, -75% player damage, altered enemy spawns

I absolutely detest Bethesda's "sliding damage" difficulty settings. It's possibly the worst adjustable difficulty model I've ever seen, as it punishes those who want more challenging gameplay with more tedious gameplay instead. Increase enemy spawns as difficulty is upped. Give them better equipment/stats. Increase their detection radius, cone of vision and their "notice stuff threshold". Make them "link" if their friends are attacked. Anything is better than "make the same schmucks you fight on Normal take 8x longer to kill".

Thankfully, that's what mods are for.

its difficult balancing difficulty (since we cannot "improve on ai") just on one end, cause you will end up with all enemies one shotting you which would be very frustrating

Yeah, but if you can one shot them as well, then everything is fine and dandy. You'd actually have to play for survival and not just run and gun. The hardest difficulty would actually be for those that wanted a great challenge. Normal difficulty would still be normal.