The chatter from all of them, and the likely interference on channels has got to have a noticeable effect on bandwidth. Wow. Trowing in a few switches should help, but using wire for connections between AP's is the way to go.Very much overkill. All of your Access Points are connecting wirelessly to the router (the dotted line connections in the screenshot indicate this). This means, much of the WiFi capacity is being split between client and uplink tasks.
If you have a large facility you are trying to cover, the number of Access Points may be ok, but if you could connect them via Ethernet to the router, you would have better performance. That would allow up to 1Gbps uplinks from Extremes and Time Capsules to the router, 100Mbps for Expresses. If direct Ethernet is not possible, powerline or MOCA adapters can get Ethernet to remote locations, generally in the 300Mbps - 1Gbps range.
In addition to performance hits from the sharing of WiFi radios (client + uplink), you may have a lot of interference from radios operating on the same channels as belvdr suggests, they tend to interfere with each other and slow things down considerably.
When it comes to WiFi, less is almost always better. Commercial grade gear is designed to deal with the contention of high concentrations of WiFi access points, but Airports don't play in that arena.
A little more detail on the reasons for so many Airports, the challenges you are trying to overcome, and current performance results might help get some constructive guidance.
Jesus, get a Netgear Orbi.
Exactly. Using Apple airport gear like this is idiotic.When it comes to WiFi, less is almost always better. Commercial grade gear is designed to deal with the contention of high concentrations of WiFi access points, but Airports don't play in that arena.