I think everyone has their opinions on this. Personally, I think a lot depends upon the cats themselves, what they are used to, their personalities, ages, living situations etc. I think there is something to be said for both ways and everything inbetween, but personally, I would side with caution, taking it slowly step by step if needed,which in this case, I would probably go somewhat slowly but moving onto the next step if it goes well. Due to the hissing I would put the resident cat in the room like stated above, at least for a while, switching back and forth until everyone is used to the scents. Also rub the cats with a towel or something, or use their bedding and rub it around the house, where the cats lay, mingling their scents. I was very lucky, I did just "throw" my cats together (although I did try separating them but because of our very small home it was pretty tough. We don't have empty rooms). When we got Lewis last year I had a nice little place set up and was going to do everything perfectly....Well, that lasted about 5 minutes because he got out of our bedroom. And when he was in the bedroom, Wallace and Marcellus were VERY curious...no agression or hissing when they sniffed noses under the door. All 3 cats were meowing, not meanly,more like..Hey, I want to see you! Then Lewis got out and they all started sniffing. We were most lucky though as Marcellus and Wallace took to him instantly and within the day they were all buds, wrestling and having a grand old time together and still are to this day. Marcellus wanted to play immediately. We got Marcellus at 8 weeks and then we got Wallace when they were both 6 months, still kittens), Marcellus was the happiest cat in the world, I swear. He ran over to Wallace and if cats could talk, I think he would have said, "Thank you for bringing me a friend." They are buds. We had no problems. However...I KNOW this isn't the case with every cat and age and personality really do matter. Some cats never become buddies and only learn to tolerate each other, if that. My point, it wasn't necessary for us to take all those steps but for some cats it is, especially if you want them to get along. It seems that one should start out on the cautious side, taking it step by step, reading your cats cues very carefully, but feeling free to bystep steps if all is going well and if it doesn't go well to slow down. One thing I did do was put a dab of vanilla by their necks, under their chins and at the base of their tails. I think that helped too. I do that when they go to the vet also. Good luck with your new kitten! Everytime someone writes about kittens it just makes me want another. I just love kittens.