I just use one aerial connector and it's fine, and also picks up all of the TMC information too -
Once you've got the MDI kit you can connect up either a USB lead so you can run another external Hard Drive or an iPod lead to be able to fully browse your ipod, I've got mine wired so the lead comes into the glovebox - although you can't watch videos from the ipod. You can watch DVD's through the normal CD/DVD drive though.
If you already have Bluetooth your phone will work through it fine as it does with the standard headunit - if you want to be able to dial & view contact numbers on the screen though you'll need to install the premium bluetooth kit.