Old Airport Extreme as a bridge
I have an airport extreme (A1354) and I was wondering if I decide to purchase a new airport extreme, could I use the old one as a bridge
If by bridge you mean can the Extreme be reconfigured as a wireless Ethernet bridge, then the answer is no. Only the 802.11n AirPort Express can be used in this fashion.
However, it can still be configured as a bridge when used in conjuction with other AirPort base stations in either an extended or roaming network.