1. Since you separated your SMS and Email Inboxes then you should now have the main Messages folder (where all new emails go) and SMS and MMS (where they all go). Sometimes, the separation doesn't work on some themes.
2. As for AIM, let's wait for the other folks and what they have to say. I have only used JiveTalk since Day One.
3. You sure can put MP3 and use it as a ringtone >
How do I get ringtones on my BlackBerry? - BlackBerryFAQ and/or you could just Bluetooth some and go into Profiles so you can set which MP3 you'd like to use as a ringtone.
4. I think it's been answered.