He's so handsome! I love the 4th picture. =]
Haha, and Lilly(my (well, actually my dad's) cockatiel) loves the toy Tiki is standing on in the first picture, since we bought one for her. She'll play with it for hours!

In my experiance, for relatively calm birds like Tiels(& budgies), they're not hard to introduce at all. Just don't forget to put the new bird through quarantine first. You wouldn't want to bring a disease into the flock by accident.
With most of the birds I've worked with, sexes didn't really matter. Though, of course, all birds are different.

If you need details on how to introduce birds, just PM me. =D I've introduced lovebirds here at the house, and countless species at the store, so I pretty much know the drill.