My home contains about two computers and two laptops (me and my brother both have PCs - my mom has a laptop she uses here sometimes and my sister has a laptop and uses it whenever she's home). We networked them all together - wirelessly, apart from my PC, which has the main modem and wireless gateway, so it gets a hard line.
Since we have so many hard drives, I just put copies of my super, ultra important files on each computer. That's what you said you were going to do and should do. To add to that, buy a backup program. When I got my new PC, it came with a backup program service, and I've used it, and it lets you restore your old hard drive. Very useful. Sure, it costs money, but it's way useful.
That should keep your "important files" safe

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