Hi guys, I wish to do the Dark Brotherhood quest line, but I am worry it might involved killing some NPCs that offer quests and stories.

Would I be killing some NPCs off that offers quests and rewards? Or Should I leave this quest line to the last?

In some cases, yes, but they are generally minor quests.

I think there is only one. The begger in Ivarstead. So go and do his quest first, before you assasinate him.

Also the Vici chick you have to kill during her wedding. She's part of the misc quest for the Wine vendor in Solitude.

Ah yes. That Alto Wine that you can't get out of your inventory. Ever. Just kill the b****.

Your question has basically been answered, but if you're worried just look up each target by name in a wiki to see what quest(s) they may offer. I'm assuming, since nothing is time sensitive, you can do the target's quest even if you have their contract active.