You can almost always make it more redundant. From what I see in your post, the next point you would add redundancy would be by adding a second firewall that provides a backup for the main firewall. If you want full redundancy, you need to avoid any single point of failure, so every piece of equipment would need to be duplicated, on separate power sources, using separate paths for the network cables (ideally with the equipment in different buildings), and dual internet connections with different entry points into the building.

How much redundancy is worth it depends on the situation.