Two bridge and STP

Hello, my LAN today has this topology:

[router]

    |

[bridge]
|
[switch]

[bridge] is a Linux box with 3 NIC, 2 of them are a bridge (br0) with IPtables for firewalling. The other nic is for management.

I want to have a standby
backup for [bridge] in case of failure. I've read some documentation and I came in conclusion that the new topoligy will be:

      [router]
            |

      [switch]
      |           |

[bridge] [bridge2]
| |

[switch]

with the two bridges STP enabled.

I think I had to:

-
install bridge2 configured as bridge
- rsync firewall rules between the two
bridges
- enable STP protocol on both bridges
- assign a lower STP priority to
[bridge] to became master
-... enjoy?

Are my assumpions correct?