Hi
Thats a fairly common bearing to fail. to start with you will want to undo the chain, there should be a joining link somewhere. To change the bearing you will need to remove the drive assembly, so that just means undoing the bearings on both sides from the frame.
You will need to remove the belt tensioner (the sliding pulley bit that goes from under the battery to the back of the frame, i see the belt is already off), forward reverse linkage (one bolt from underneath, has locknut on top).
Once all that is undone you should be able to take the pulley assembly out the top of the frame. Once out undo the grub screws, and you will probably need a small gear puller to remove the sprocket and then the inner bearing race from the shaft.
As for the electrical system, some photos will help, I could never understand why people would complicate such a simple starting system, but i'm sure it should be an easy fix.
