Sorry for the maybe stupid question but

I just started a few minutes of playing and searched already but only found some short hints.

How exactly do I work with thr traits?

Can someone tell me: how do I use, for example, the interactions?

I have a dominant dark elf and some human girls with nice voice and stuff

is there any way to interact multiple times per day with different slaves?

because right now its only 1 slave/day

How do I know what the slave need/likes?

Chat seems to work with all but not forever and how do I then continue from there?

Can I also lower the difficulty or add ressources for pure enjoyment of story and slave interaction?

right now (at the start) it seems to just interact and eat, end a day, interact and eat, end the day. and so on....

Traits mostly give the slave a bonus or malus to certain occupations or tasks. Pretty Voice gives a bonus to charm and social jobs. Strong increases strength which is useful in combat. Scarred decreases beauty and charm, so it will decrease the cost of a slave and in an job where looks don't count such Mage Order Assistant can result in getting a useful slave for cheap.
The number of interacts the PC can do is based on their endurance. Increase your endurance and thenumberof potential encounters will increase. 
Mostly slaves all like the same things, your attention, gifts and so on. However if a slaves loyalty and obediance are low, you need to stick chating and maybe hand holding. Gradually their obediance and loyal will increase. Alternately, you can beat them until their obediance and fear goes up. The Maid and Butler outfits increase obediance a little at the end of each day.
You can try the sandbox mode instead of the story mode when begining a new game. You will start with more resources and will already be a mage guild member.
At the very beginning, set your first slave to Hunt. They won't be very good at it but usually can feed two people. Go onto town and try to complete a slave guild quest or two. This will give you money, experiance points, mansion upgrade points, and increase your reputation. Check the Mage Guild, completing the initial quest will give you membership and a useful spell.
Don't try to get a bunch of slaves right at the beginning. They will be hard to manage and not bring in much money. Give yourself time to gain a level or two (remember to increase your endurance) and get a cushion of money farming captured bandits and completing slave guild quests.

didnt read amberpost, big textwall >.>

interactions: 

mode:meet - is to unlock sexual actions, teach the slaves, get obedience and loyalty up, give punishment. Try first to unlock sexual actions, cause the others will be more efficient after that. I would give you a pass-to-pass, but it would be no fun, is better for you to discover the wonders of teaching slave.

mode:sex - gives you mana and loyalty, can only be used at slaves with sex unlocked.

mode:other - have fun discovering.

you will get to understand traits with time,  dont bother too much with it in the beginning.

I'd reccommend you use the girl with pretty voice as w - entertainer if she has grade of commoner or above.

and give the dark elf to the brothel at red light district or find another elf to give if you wanna keep it, doesnt matter if its male/female

endurance will add one more interaction point each odd number, like, with 1 end, you get 2 interactions, with 3 end, 3 interaction, with 5 end, 4 interactions,with 7, 5 interactions, you can only go past 7 end with items boosting it.

if you are starting, I recommend you do like this:

put someone to hunt... whoever has higher courage.

put someone to cook... agi and wits affects it, but its not much important in the beginning, this should be enough to keep you alive.

w - prostituition is the most lucrative work  at the beginning, w - escort being the second... but both need sex unlocked, this means, you need to have sex with the slave. Charm, end and beauty are the best stats to w - prostituition, if charm is 60+ and looks 40+ and it doesnt have any traits agaisnt (prude, monogamous, just mouse of the trait, it will tell if so) is worthy buying slave to work on it. It will rend you around 150g per day, the higher the stats the more you will get.

w - escort - needs grade commoner or above. If theres is no trait against prostituition, Charm 60+, Confidence 50+, beauty 40+ its worthy buying a slave to work on it.

remember to make then sterile with "services for slave" at the slave guild or just sell then if they get pregnant.

if you are luck to find slaves with str 2+ and end 2+  at the guild, you may consider buying up to two of them, so you can go out of town. If they can be used to the above work, use then, if not, you can aways put then to do something, just have fun there is no need to hesitate, at worse you will start again.