I have spent a significant amount of time in the last few weeks making my AirPort network somewhat reliable and stable. I have had an uptime so far of 7 days on my ActionTec router and the network has been extremely stable. Even the wireless printers have been stable.
This is what I have:
1 - Telus ActionTec T3200 Router served by a Telus ONT with a 300/300 mbs up and down
1 - AirPort Time Capsule - latest gen
1 - Airpot Extreme - latest gen
2 - Time Capsules 1st gen. (one has the PS removed and soldered in wiring for external PS)
I have all but one 1st gen Time Capsule Creating wireless networks with channel selection in automatic and I have analyzed my spectrum and it appears the auto setting works quite well. I have no overlap.
What I have learned through lots of trial and error:
Telus does not issue IPv6 to Airports.
Telus OptikTV does not work with Airport Routers - even with IGMP Snooping Selected
Even if you put a unmanaged with between the Telus ONT and the Airport to split off the Optik TV, you do not get IPv6 addresses. Telus Optik TV does work in this configuration.
Use the Telus ActionTec router as your main router. This is the only way to get IPv6 reliably.
Turn off the wireless on your ActionTec and only use the Airport Wireless. Unless you have Wireless OptikTV, only use the ActionTec wireless for OptikTV.
Designate ONE Airport to connect to the ActionTec router.
Connect that ONE Airport Router to the ActionTec and all other Airports downstream of that designated Airport Router. I was connecting all the Airports into the ActionTec (thinking that this would help speed up the network) and this was causing issues with Airport utility not being able to find other Airports on the network after an indeterminate amount of time - sometimes an hour sometimes a day....
Use ethernet between all Airports if possible.
Use static IPs and DHCP Reservations for all Bonjour sleep proxy devices. (Airports and AppleTVs)
Use Static IPs and DHCP reservations for all wireless printers. This help with reconnection when those devices go into sleep mode. I'm assuming....
Moving into the future, I will look at upgrading all Airports to Ubiquiti APs and routers.... After all Airpots are at least 5 years old...... And I will connect an external USB to my MacMini for network Time Machine backup storage. I may consider a Synology NAS, but those are quite expensive and if macOS has designating a external hard dive for network backups, this may be a great way to go.
As for Time Machine, I think this may be phased out in the not so distant future as more and more stuff is being moved to the cloud. Seems as though this is the way that Apple is moving and everyone else for that matter.