Airport Extreme Roaming x Multiple Base Stations

... Is there any reason that the Airport Extremes couldn't simply be connected via Ethernet to our existing wired infrastructure and have each one be part of the same roaming network with one SSID?

No, none at all. You need to designate a router, which may or may not be an Extreme. All other access points should configured as bridges. They can be either Extremes or the less expensive Express.

Apple used to recommend a limit of 50 wireless clients for the Extreme. I can't find any limit in recently published specifications though.

Wi-Fi base stations: Setting up and configuring a roaming network (802.11 a/b/g/n):

http://support.apple.com/kb/HT4260

Apple used to recommend a limit of 50 wireless clients for the Extreme. I can't find any limit in recently published specifications though.

I've heard different stories on this as well. On the one hand I've been told it's 50, on the other hand I keep being told the theoretical limit is infinite.

I do know when I speak to some of the tenured advisors (over half a decade experience) they've leaned on the infinite side. Obiously, there is still a limit somewhere in there during practice. But I agree that there should not be some sort of hard-coded limit here as we are not exactly talking about USB limitations.

I may try to send some messages to engineering sometime this week and see if there is a more definite ruling on this.

Apple's literature pretty clearly states 50 users for the AirPort Extreme. We had no trouble getting 50 users connected at my grandson's school, but it was really "iffy" when we tried to go to 51.

Even if you stay at 50 users, they must all share the bandwidth available on the network, so depending on your Internet connection, it might be wise to be as conservative as possible.

With 2 AirPort Extremes connected using Ethernet, the total would rise to 100 users, but everyone will get an even smaller slice of the already very small pie.

http://www.apple.com/airportextreme/features/wi-fi.html

Very late reply, but:

There's no hard coded limit to the number of users apart from the number of IPs available if you're using an Airport as a DHCP server.

The size of the routing table is fairly small as well. If the Airport is used as a router, you're likely to run up against that and you'll begin to see connections dropped inexplicably. This will vary based on mode of use, of course. A bunch of people browsing the web may never see an issue, while a single user with a lot of P2P connections from Skype or a file sharing client can exhaust the table singlehandedly.