Two main issues:
1. To install the OS from a flash drive, you'd need a slipstreamed image of Windows 7 which includes some missing drivers. This can be found, along with detailed instructions, if you search the forums here. Depending on your exact system configuration and which download you obtain, you could run into additional unforeseen complications. Some people manage it quite easily, and others have all sorts of issues.
Alternatively, if you want to install from DVD, you'd need to have a motherboard with a PS/2 connector (ideally two, for keyboard and mouse,) a keyboard (and mouse if possible) with the correct plug for that, and an optical drive installed.
2. Microsoft will be discontinuing support for Windows 7 in early 2018 on Skylake machines. I've now heard half a dozen versions of exactly what that means, ranging from "no Windows updates at all after 2018" to "security-related updates will continue until 2020, unless it's for an issue that's specific to Skylake (which is fairly rare.)" But I've yet to see a very detailed explanation issued by Microsoft itself.