Hun-hun, I do believe your friend can read English(especially if she's corresponding with an American, which I assume you are), so unless you really want to write in Russian, I suggest you do it in English. Why? It is just more special to receive something written in a foreign language from a foreign land that you can read and understand. I treasure all of the cards Russians have sent me because they're written in Russian and it is just neat to have something like that lying around - friends ask me "Hey, where is this from?" Much neater than a bunch of cards written in English lying around, anyway. If you write it in simple English she should understand just fine.

About "Here is my boyfriend, he's such a sweetheart", why have you translated it as he is "классный"? Wouldn't that make him more "cool" than "sweetheart-y"?
Also, make sure you throw in some transliterated version of Brian too - Это мой парень Брайан, он такой....err....милый? Голубчик? Рыбка?

This is my friend.....Name? It makes things a little bit more interesting.