Before we got Sophie, I had a lot of the same concerns about my Tito you have about Mischka. We have a small apartment too, and the shelter I got Tito from warned me he was "not good with other cats," and I was SO worried about his personality changing with the addition of a new cat. Everything ended up working out better than I had hoped. Tito ended up being fine with Sophie, nothing more than play fighting (unless it's a dispute over who get to eat the cat grass!! ) and he's the same old sweetheart he always was. I think introducing a kitten to an older cat is easier than you'd think, like CCL and Catnapper have said. I say go for it. Mishka will probably be fine, he'll just require some extra lovins!!

By the way, my (now RB) cat's name growing up was Mushka!! Mishka is the only name I have ever heard even similar to Mushka. My dad named Mushka before I was born, so I have no clue what it means (I'll have to ask). I'll post a pic of him sometime...as soon as my boyfriend hooks up his scanner!!