My recommendation would be to go for a simple airport extreme to run the network. Time Capsules take ages to sync multiple devices and when accessing the backups have been known to crash when dealing with more than one thing.
The thing to note about the TC and Airport Extreme is that they don't have a built in modem so you will need a modem box anyway. The ISP supplied modem routers are good enough for purpose, but you will need to know how to put it in bridge mode so the ISPs router/modem does not start trying to assign the IPs and manage traffic.
As for why your iPads cannot keep a wifi contact, is this a constant thing that drops randomly during use or does it happen every time you turn your iPad off and on? If the latter then it is poss that the primitive router
you are currently using is assigning multiple devices the same IP address, 2 devices cannot function online with the same IP and it causes crashes and dropouts a plenty, way round this is to assign a static IP range to your known devices and stipulate another range outside that for guest/unknown devices.
Hope this helps Slinky