As a relatively new bird owner, I'm not very qualified to offer advice. I can however, share my experiences with you. It's been a few months since I last posted in this thread.
I have a TAG and a Sun Conure. My TAG is 14 and we got him this year from a local rescue. Even though we got him from a rescue, I don't think he needed rescuing, he just needed a new home. This is obviously my first Grey, and I was scared to death to even get him after hearing all about how neurotic and needy greys can be.
My Sun conure drives my TAG a little crazy. She steals his food, and will occasionally go into his cage. He gives her hell, but knows she's part of the flock, and certainly doesn't try to kill her. The Sun doesn't try to hurt the grey either. They occasionally do the same as Tom's birds when they are both on the same person - the snapping and show on who gets which shoulder. They do compete a bit for attention, but I give them both attention at the same time, and separately. I think they seem happy with that arrangement.
I went into multiple species ownership with the hope they would be friends, the expectation that they could co-exist at least, and the knowledge that they may hate each other and try to kill one another. I have a co-existing situation in my home, but I'm hoping that maybe one day, they will be actual friends. I know for a fact that although they aren't buddies, they interract from their cages when no one is at home. (seen it on my spycam) So I conclude that birds do enjoy the company of other species of birds, even if they don't get along outside of their cages.
I have a tall cage for my grey (not sure of dimensions), but he almost never uses the playtop which is about 6' above the floor. He prefers to sit on the top, or on the open door. I'm not sure about the eye height thing. I know that my TAG is definitely more nervous, and does like to be above the flutter of legs and such (I also have 2 little kids). Perhaps that is the reasoning - they don't like sudden or quick movements.
I am lucky that my TAG is not a biter. But that being said, he does have specific warning signs if he's not interested in interacting. Body language seems to be more obvious and exaggerated than that of my Sun conure. I also learned that eye pinning in my Grey is common, and doesn't necessarily mean a darned thing! My Sun conure picks up tricks in only a couple of tries, whereas my TAG seems to take longer, and is far more reluctant to perform any tricks. Due I assume, to higher intelligence?? My Sun is a quintessential lady, and rarely poops away from her cage, and NEVER on a person!! My TAG lets fly wherever and whenever the mood strikes him. We are trying to work on it, but he's not really interested in learning.
The clipping question is one that only you can answer. There are many people that argue for or against it. IMO, if you get a new bird (not a baby) you should clip it at first so you get the opportunity to learn about each other, and it can get used to your home and routine. The wings grow in after about a year, and the bird molts anyways, so then you may have established a routine, gotten comfortable with each other, and know what to expect somewhat from each other. But again this is my opinion, and I'm sure others would have arguments the other way. My TAG is clipped, but still manages a controlled glide for 10 or so feet. He has no issues getting around clipped, even though we suspect that he may have been flighted all his life. When he molts, we will allow him flight until he gets unruly.
I have attached pics of my birds, and my TAG cage just to give you some reference. (and who can resist posting pics of their birds??!)
This is them enjoying food on top of Darwin's cage, out of the same dish!
This is Darwin's cage.