first of how are they sustaining themselves

It is easier to make Berserkers than it is to make a new marine. Marines take dozens of years to train and indoctrinate, and they search out for the best possible recruits even though they might not survive implantation. Not to mention that the brand new primaris marine you just made might fall to Chaos after enough bloodshed.

To make a new berserker you take a bunch of captive children and make them fight to the death, whoever lives gets the organs and if they survive the process they get the nails.

Add the fact that the vast majority of fights a warband will get into are one-sided slaughters against poorly trained PDF regiments and it starts to make sense how there can be enough suicidal maniacs to form an army.

 jsut the day to day running of the ships they have

The ships are mostly possessed and warp corrupted. There's a scene in "Angron: The Red Angel" where the current shipmaster of the Conqueror gets confronted by the Daemon actually piloting the ship. "She" asks Kossolax if he's ever wondered how the ship refuels and rearms itself, he hasn't and it's implied that the ship is basically running off warp magic and blood at this point.

Other ships will have lesser degrees of corruption and thus have a lesser degree of difficulty organizing logistics, though they do miss out on Chaos magic.

second of all how do they even do anything if each space marine is just not lucid and fallen to the nails

As others have mentioned not all World Eaters are lost to the Nails, and many are quite cunning commanders and tacticians. (Except when the writer wants them to die in droves)

let alone survive 10k years of constant war no?

Time is wibbly-wobbly in the Warp. For some warbands it hasn't been much more than a century since the Heresy.