Have you tried finasteride and minoxidil?? (Propecia and Rogaine)
I would consider that first, even if you get HT you are recommended to be on finasteride months prior to your procedure - at least I was. Anyway, 6000 grafts are a lot and I would say that would take two or three sessions. The key for you is planning. You need to use those grafts wisely as they are limited.
I know you would like a full head of hair asap, (who here wouldn't?) however, Most NW 6 patients will never acheive that, the best they can hope for is the illusion of a full head of hair.
Their are some great comebacks from NW 6 on this forum: Jotronic, Bobman and Bill. They were cases who either had great donor, laxity or thick hair shafts and they had a lot of grafts done.
Big commitment if you go down that road and no guarantee to look just like them, just keep that in mind. Thier are risks, what if NW7 is in the future? It is hard to predict but it can happen, this is why waiting some is not a bad idea. It would be best for you consult with a few docs (only the most ethical ones) as to your future planning.
As for cricketlover, I said to hold off, I never said wait till 30 though. Maybe someon else suggested that. I think in the mid-late 20s you have an fairly good idea where you are heading on the scale.