If you mean what are they for, those tell the game what versions of the relevant body parts to display. For instance, Rogue has the following options for eyes: normal, sexy, closed, surprised, side, stunned, down, manic, squint
For brows she has: normal, angry, sad, surprised, confused
For mouth she has: normal, lipbite, sucking, kiss, sad, smile, surprised, tongue, grimace
Essentially, these work together to determine a girl's expression (though other factors like blush or if mouth is in the spunk list also impact things). Most likely the other girls use the same list of options, though I've not confirmed it, so there might be some additional or missing options for specific characters. If an invalid option is used, it defaults to normal.
As of the latest update, they will always make a comment about warning them if you cum on their face or breasts and did not warn them first. Mind, you can't warn them and choose that you want to cum on those spots. However, there isn't any negative impacts on relationship for doing so.
That is correct. All you can do at the party is move between girls and flirt. However, you don't seem to have the usual 1 flirt attempt per time period per girl. Instead you seem to be able to flirt with girls repeatedly until you either leave the party or run out of time and it ends on its own, at which point you can pick a girl to leave with (and potentially sleep with after the party).
