Don't have to remove the wheels to access the plug. It does help if you turn them to the left or right for better access, but still not necessary.
No. The clicking indicates a worn birfield joint.
Worn internal seal are evidence by having oil dripping from the bottom of the knuckle housing onto the inside of the tires or the ground.
Normal is a shiny greasy surface on the ball with a ridge of dirty grease piled on the face of the knuckle housing facing the inside of the truck.
If the balls are dry and rusty you need grease in the knuckles and need to check oil level in the differential.
Looks like this has a shiny "greasy" surface with the dirt on the knuckle housing? May looks like it just needs a good repacking at the moment?