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.
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.