EDIT: missed that you mentioned the backlight type. You may need to cut the housing for the LCD. He left this out of his tutorial for some reason.
You can solder to the 5v source on the front board. You can use the same solder points that the VB/VC backlights use.
The wire over the back of the speaker won't work. I'm pretty sure the speaker sits flush on the plastic, so the wire won't allow for it to close properly.