You only get attacked if you turn into the VL form infront of people or if people see you.
4 levels..you don't get attacked at any level anymore at level 4 no one will talk to you though.
Vampire's seduction now makes people your temporary thralls and allows you to feed on them at will be they awake or asleep...also the new Volkihar Vampires look epic compared to the old skyrim vampires not even counting the Vampire Lord form they can turn into..
Oh and if you want details..
Old vampires as you probably know were just sorta pale skinned with red and black eyes.
New vampires have glowing gold/amber eyes..paler skin and blood stained lips.
You don't take damage from the sun by the way, you only get reduced HP/stamina/ and magicka regen but items can negate the negative effects.
Sun still nerfs you and Serana through the hood.