If improving your Wi-Fi signal and range is your key goal then you need to look at the latest mesh Wi-Fi systems. Items like the Netgear Orbi, TP-Link Deco, BT Whole Home Wi-Fi, or link sys Velop are worth investigating. Remember for many of these Mesh systems they are better when they replace your existing router. This may require switching an ISP supplied router into "Modem" mode. If set in router mode you may have issues with double NAT (where your IP address is translated twice).
The Time Capsule is a great backup option for Mac users but is not being actively developed by Apple any longer. More flexibility can be obtained by using a NAS (Network Attached Storage) device, such as the Synology DS212J (fitted with a pair of suitable 2TB disks). This can also be used with a Mac or PC for backup (also supporting Apple time Machine) but also works as a media server to stream your media to suitable devices (TV, Xbox 360, PS3 and AV receivers). Note any Windows PC that has a network disk needs separate backup software as the Windows Backup program will only work with local disks. A workaround is to use VHD (virtual hard disks) if you have Windows 7 but needs some work to enable auto mounting of the VHD. I would suggest you upgrade to Windows 8 or ideally buy a new Windows 8 machine as this will make life easier.
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