Hihi Em,
Fancy meeting you here as well as on AnAG! 
First things first, though. 9 weeks is, IMHO
way too young to be getting
any parrot! It is essential that a young birds spends time with it nestmates, peers and parents for it to learn that it IS a bird, and NOT a human being. Taking birds from their parents so young can cause psychological problems later in life. Ideally, you should wait until at least 16 weeks, if not 20. See if you can't get the breeder to keep the youngster for longer -
please: it is so very important!
In principle, there shouldn't be any problem having a QP and a Grey together. My QP,
Insect, gets on fine with my 6 Greys. Well, at least, he is quick enough to be able to get away from them! But you will have to keep a close eye on them.
You will need to introduce them very carefully!
Sensei (that is the name of your Grey, isn't it) is a MUCH larger bird and he has already staked his claim of your home as his territory. A small, green intruder may be seen as something that needs to be 'disposed of'.
You must get as large a cage as you possibly can for your QP. Greys are much larger than QPs, but Greys climb more than they fly. QPs, being long-tailed parrots, are great fliers. We take Insect to Parrot Society meetings in a village hall in Shirebrook, not far from us, where he gets to fly around to his heart's content. The little hooligan is like a rocket! Flying really is important for their physical and psychological welfare, so make sure you get the largest cage possible!
As soon as you have the cage, put it, in the same room as your Grey's cage. Greys are notoriously averse to change in their environment, so the sooner you can get the empty cage in there, the better, so that he can get used to it. The cage needs to be at the
opposite end of the room from your Grey's cage.
When you get your QP youngster, put it in the cage and let them both observe each other for a few days. It is important that you follow your normal routine with Sensei. Over the course of a few days, you can adapt it slowly to include more and more of your QP. During this time, it is very important that you make a little extra fuss of your Grey, so that he knows that he is not being sidelined. Greys are intelligent enough to behave like jealous kids!
Leave the cages as they are for a couple of weeks, before starting to move them gradually closer and closer - and I'm talking just a couple of feet per week, here. Eventually, you should have both cages next to each other - close, buut not so close that one can stick its beak through the bars and bite the feet of the other, which they
will do, without fail!
Now leave them there for a couple more weeks. Observe them closely. If they perch and roost in their separate cages in such a way that they are sitting as close together as possible, then you have introduced them successfully and they have accepted each other. You can then try letting them out together - but have a towel handy so that you can break up any brawls that may occur, and remember that a Grey is SO much larger than a QP, so you must act QUICKLY!
If, on the other hand, they sit at opposite ends of their cages, trying to get as far as possible away from each other, then you will have to consider the fact that they will never get on, and you will need to modify their daily routines so that they both get quality out-of-cage time and time with you.
Working 8 hours a day is not a problem. As long as you have a daily routine and
stick with it, they will be perfectly happy.
Hope that helps.