This diagram shows its legal moves a few moves after it has moved to 4. At this point, it may move to b3 but not back to c1. Is this all correct?
The move options shown are correct.
The possible moves of a bishop on 4 go in the direction of d1 or e8, but not to a3, b2 or c1.
Here are some examples that are not handled clearly enough in the description of the rules. The following diagram shows legal moves for the Bishop on c1. It can move to 4, though not to a4.
These moves are not possible.
The bishop on c1 can move to a3, but not into the switch. The bishop on 4 can in principle move to d1 or e8. The moves to a3, b2 or d1 are not possible. The queen on d1 can reach the switch - provided there is nothing in between. In the switch, the queen can be on 4 or a4.
The move options shown are correct.
The possible moves of a bishop on 4 go in the direction of d1 or e8, but not to a3, b2 or c1.
These moves are not possible.
The bishop on c1 can move to a3, but not into the switch. The bishop on 4 can in principle move to d1 or e8. The moves to a3, b2 or d1 are not possible. The queen on d1 can reach the switch - provided there is nothing in between. In the switch, the queen can be on 4 or a4.