<cracking knuckles>
ah, my boy. Wanting to join the elite club of those of use with NUTS big enough to try expensive beautiful fish!!! Your application will happily be accepted.
Emperor angels are a great addition for an angel tank. They are actually quite hardy, if they can survive the initial Ich he will likely get. Make sure the one you get is eating and an adult about 5 inches long. You may have a better chance of survival with a juvenile, but they take SO LONG to change and that is what you really want is an adult. They do not get along with other Pomacanthus angels unless your tank is bigger than 180. I am going to risk two in a 265 and I don't know if that is enough space.
I have a sohal with my koran and blue angel. He is the king of the tank, but is so pretty, he is worth it. Sohals, once they get about 5 inches will kill most tangs they encounter unless they are significantly larger than the sohal or in a system that is abusively large - say 600 gallons or so. I think the sohal / pomacanthus mix is perfect since they are both aggressive. they tend to ignore each other, at least mine have for the last year and a half.
You CAN keep more than one angel in a tank. I have instructed Redline how to do it and he has two in his 180. I have 4 in my 125 (don't worry, it may be getting bit tight, but they will have all kinds of room in a few months). Pomacanthus mixes well with Holacanthus (passar angel, blue, queen, etc). Each variety of angelfish has it own personality set within the family. So, for example, a majestic (navarchus) angel is a passive angel and will actually do great with another passive pomacanthus angel in a 180, like a blue-face angelfish. Certain pomacanthus angels are just assholes (Grey, french, blue ring) and cannot be kept with any other angelfish. It just depends on what you want to try.
best success comes with placing a smaller angel first, followed by a much larger, different family and coloration angel, like Redline did with a Koran (small) and a queen (Huge). there will be some nipping to remind the small one who is king, but it is mild and never causes major damage. Hope this helped.
-Doc