Having a small and large bird in the same house - How chaotic/hard is it?

I have a male, 5 year old nanday conure. He is very placid, easy going and friendly. Loves everyone who walks in the house and isn't phased by other animals. I have been thinking about a second bird for almost a year now... But I only have one type of birds I'm interested in... I'm hoping someone will be able to shed some light on what I could expect from adding a second or if I even should go ahead with it.

Now, the type of bird I REALLY want and have wanted for a long time is a galah (rose breasted cockatoo). I love everything about them. Their colour, their cockatoo craziness, their crests, their floofyness, their voices and their size. I love seeing them in the wild and feeding local flocks. I just love 'em! I am falling in love with a rescue Galah at our local shelter. He's 23 years old and completely adorable. He is a little shy, but warms up to you when you spend time with him. He's an aviary with a corella and cockatiels at the moment, so he seems OK around other birds? I would adopt him in a heartbeat if I wasn't worried about Spyro, my nanday. I have heard horror stories of bigger birds biting toes and beaks off smaller birds or worse, killing them. I have also heard that native Australian birds and cockatoos have "dust" in their feathers, which is bad for for South American parrots... Is that true?

If I were to own both a galah and nanday, how careful would I need to be? How quick can things turn bad? How far apart would their cages need to be? Would I need to have completely separate "out of cage time"?

Also, would it be better to get an adult galah or a baby one? I really, REALLY love this guy at the rescue.

Thanks for any info. I would love to here input from anyone who owns a larger and smaller bird in the same house!

I have never owned a cockatoo, Seen them and the rose breasted is awesome. I have a sun conure and an eclectus. The eclectus does not bother the conure;however, he will bug her at a distance. He hasnt gotten the nerve to approach her to close. She really doesnt care about him unless he makes to much noise and then she will tell him to "be quiet" if he keeps on she makes her scream and that shuts him up she is way louder when she wants to be LOL.

They eat together on my breakfast bar supervised, he is on one end and she is on the other. I also put them on their own table perch when i am watching tv or cleaning the livingroom. I never leave them alone because the possibility. My conure has attitude I love him but he can be annoying since i know he annoys her at times i never leave them unattended and once i hear her say be quiet the conure gets put up or one of my girls will take him to watch tv with them

The conure and eclectus I have their cages in different rooms only because I know the eclectus likes quiet time. I don't see an issue with a cockatoo like this because evey too i have encountered is extremly hyper and playful

I'm just now in the process of introducing my senegal to my new CAGs (vet just gave them all a clean bill of health). As of now, the sennie is determined to be a part of the flock, copying them and wanting in their cage. She even fluffs up excitedly when they're near and she things they can give scritches. The new birds... Well, they're not sure how to handle this strange new creature and give her odd looks and the occasional warning to let her know they are uncomfortable. Even if she is accepted by them, I wouldn't let them out together without supervision, since it only takes one grooming accident to loose my sennie. As long as you have enough space that they can play while being able to get away from each other, you should eventually, after several months and only if you can handle each bird expertly, be able to let them out together with supervision. This is all bird dependent of course. Some birds would wreak murder on each other if they had the chance.

I have the same issue. quite a size difference between my hahns and gcc... their cages are next to eachother so they are comfortable being close to eachother, but i havent yet dared risking actually letting them have contact... I'm not quite sure how to go about it and i know bandit can lunge if she's in "that mood" she's very unpredictable, her body language doesnt give away much, and one of her bites could seriously damage pippen...
i'd love for the two of them to get on, but so far they each keep to themselves, and since pip is fully flighted and VERY curious i dont risk having him out when bandit is out as well, cause he will fly over to her and god knows how that will end...