there is no universal standard for anything Mesh. there is no such thing as standard for anything to do with extending a wifi network. extending a wifi network is a "technology" and not a "standard". because of this, the easiest and best solution for you is to buy another airport extreme, and use airpot utility to set it as an extender.
you can ether extend the network by running a cable from the time capsule to the airport extreme or you can do it wirelessly via 5ghz. if the airport is linked to the time capsule over 5ghz, then airport utility can automatically set one of the base stations to be on a different 2.4ghz band.
i noticed this other day. i didn't know about that before. i got 5 apple wireless routers in the house and some of them are on different 2.4 channels. and i used to think that wasn't possible. wow!
what you should do is run a cable from the time capsule to the airport and then put the airport near the devices that need a better wifi signal. if you can't do this, then put the airport extreme at the half way mark and see if it helps
im not sure abut extending via ethernet cable though. i thought this was an pre airport utility 6.o feature ( like 5.6 for windows )?? airport utility 6 might only link them wirelessly. i just don't know anymore
if you can set a wired link, it would be better.
another thing about 5ghz a lot of people don't know is the FCC used to regulate power limits, and channels like 36 or so are supposed to be limited in signal strength, because they used to be considered indoor channels. so if you move the 5ghz channel to 140-161 , the signal strength may be stronger because those used to be the "outdoor channels"
[doublepost=1462766837][/doublepost]what i mean by no standard is that the overseeing body, the wifi alliance that tests and certifies products does not certify anything close to a mesh network / extender setup. because of this, it is recommended you buy your extenders from the company that made your router. even routers from the same company might not work.
the worse thing about extenders other then a lack of standard, is if you get the wrong one, it might cut your bandwidth in half.