Are they easy to connect together?
Can I connect one Time Capsule to the external world (ADSL or faster) then daisychain two or three Time Capsules using fast ethernet? Has anybody tried this?
Yes, very easy.
There is no problem running ethernet and setting the TC into roaming setup. It is actually the preferred and recommended setup.
There is even an apple document .. rather outdated.
I'd like to have redundancy - two networks. One would start at one side of the building, the other from the other side, both daisy-chained.
Does that mean you are talking about 6 TC?
Wireless has a limited number of channels.. for 2.4ghz there is only 3 non-overlapping channels, 1, 6, 11
There are more channels for 5ghz but AC uses 80mhz .. so it cuts into the channels.. I am not sure myself how many individual AC units you could setup.
The US does not allow some of the inbetween channels down low so I think your AC units are going to be forced into the higher end of the band.. so perhaps 3 separate radios.. although 5ghz is poor penetration so you can use the band over again.. for most highly spaced ones.
How well would they work together? Would there be a problem with them interfereing with each other?
The TC is not a business or industrial unit. Although people do use them you should note a few things.. management of a large number of them becomes difficult. The management tools are plainly domestic.
There is no snmp now.. and no access to the log. Apple seem to not want you to know what is going on.
Go into an apple store.. check out who they use for wireless.. it aint apple.. they get it properly done by Cisco. There are too many clients to be handled by domestic gear.
Look at Ubiquiti for a lower cost but more pro solution for large wireless installs.. than Cisco or HP.
The other thing to note is security.. you cannot tie these into a server very well. Everyone can simply press the reset and access all data on the unit.. or change the wireless name. You cannot control them.
Finally - I know that you can configure these from OS/X and Windows - what about Linux?
Actually even windows setup utility is not up to speed. Apple are dragging their feet, and they have produced no update since 5.6.1 for win7. So you cannot setup the AC models properly from windows.. Linux not at all. There is an iOS airport utility.
Compare that to the kind of management available with ubiquiti.