What setup is needed to stay backed up and online after retiring the TimeCapsule? My friend has the following kit in the house (although not all at the same time):


His MacBook Pro 15" with 500gb HD 
Her MacBook Air 13" with 256gb SSD
Daughter's MacBook white with 500gb HD
His and Hers iPad 3
His and Hers iPhone 5
Son's iPod Mini
Nanny's iPhone 4S
Grandpa has an iPhone 3GS
AirportExpress for the bathroom speakers (niiiice)
Apple TV in the lounge
XBox 360 in the lounge
Samsung Smart TV in the lounge
TimeCapsule 1TB
Western Digital dual-drive 4TB USB drive (formatted as mirrored 2TB), connected to the TimeCapsule.


The Apple TimeCapsule has recently become unreliable either failing to do TimeMachine backups or losing it's internet connection (even though it is wired to the broadband modem). Even before this, the performance of wifi TimeMachine backups was poor - 300MB of changes would not complete backup before battery ran out. I have to admit, mine is exhibiting the same behaviour.

So, he'd probably like to move away from a TimeCapsule network.

What's an alternative setup to allow all the same (or similar enough) features and functions? Does he have to buy a Mac Mini Server?

UPDATE

The internet connection works fine when we plug a Mac into the modem directly, but the TimeCapsule would not allow WiFi clients to connect, so pretty sure the TimeCapsule is at fault.
You could certainly try backing up to a computer running a server version of the OS which allows for networked TM backups to it much like your Time Capsule.

You could also just get an Airport Extreme and roll your own Time Capsule equivalent.

You could try to nail the performance issues of you TC by attaching wired to see if things improve, and it may then prove simplest to just improve your Wireless capabilities by wiring a couple of cheap Airport Expresses to it, you could then even though a cheap switch on the end of one for faster backups if you have a large one.