If I plugged a hub inbetween a switch and firewall, that also had a device running wireshark or similar capture software connected, due to the way a hub operates, would I be able to read ALL of the traffic between the switch and firewall, E.g. All inbound and outbound packets?
In theory, yes. I did this for over a year some time back. Be prepared for the possibility of this hurting your overall throughput, especially if you've got a lot of traffic and are approaching the maximum of your firewall's interface.
Another caution, at a conference where a team was going to demonstrate this using a Linksys hub, they discovered Linksys was branding some of their switches as hubs. This was > 5 years ago but I wanted to warn you to avoid potential frustration.