My opponent plays harpies in my zone, i have 6 cards, and then draw to get 7. Can He use his ability once i get 7, or do I have to have 7 cards when i draw?

The other combo he tried, is he used We need your blood, felheart, and vile soceress -hp abilities in the zero phase combined with the dark elf support that says "at the beggining of your turn, return a target unit to its owners hand that has less than 2 hp." If vile sorceress forced says at the beggining of your turn, and this building says at the beggining of your turn, how does this work?

for the - life question, he can put -X life (with fellheart or sorceress) then say "take back your unit with X+1 life in your hand" .

Not sure for the harpies (don't remember the text in my native language and I don't want to say something wrong)

I'd say it works, the trigger is drawing cards for Quest phase, and when Harpie's action resolves, your opponent has 7 cards, so it's a valid target.

For the -life question, Vile Sorceress action is forced, so it's the first being played, then he can use the other 3 actions in the order he wants, so wisely used, he can do that combo.

Yes to both.

Heres my reasoning for Harpies. Lets say a card says this " When an opponent shoots his basketball, if he has 7 or more points, discard one of his cards." Lets say Shooting my basketball is "drawing cards for my quest phase". If my basketball goes in the hoop and gives me 7 points, it shouldn't matter, because the trigger was drawing cards, or shooting the basketball. Or am I really wrong?

Your analogy is wrong. Change it from shooting the ball to score a basket, do you see the difference?

Okay, here's where things get a bit weird. James informed me that damage on units does NOT reduce their HPs actually. It's just damage, nothing more. Kind of a weird bit of info but interesting nonetheless....

That doesn't seem weird to me. If damage reduced their HP's what happens when they are healed? Healing removes damage but does not add HP otherwise you could use it to add HP to a unit that is undamaged.