Stick with FreeBSD and use ZFS. It includes filesystem-level checksumming, deduplication (just rolled into STABLE) and encryption (still in CURRENT) http://en.wikipedia.org/wiki/ZFS http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/filesystems-zfs.html
If you have line of sight (or can bounce off a neighbor, tree, kitty...) WiFi is the quickest and easiest way. The cablemodem is probably 10dBmV, put the amp at your end. You can look up the signal strength and frequency on his modem, then calculate the splitters, cable loss etc. accordingly. With the amplification figures, make sure your modem will get at least -15dBmV (not more than +15dBmV) on the forward path, and ensure it won't have to transmit more than 55dBmV for return (lower is better here). The return frequency is quite low so should have less than 10dB of loss, just watch out for crossing any electrical as it will induce noise. You could lay it on the ground, risking damage to tha cable, or get direct-burial cable that will go bad in 10-15yrs. Best bet is conduit, even 1" stuff that comes with cable inside and can be put ~6" in the ground by a trencher pretty darn quick. Pay someone to put very good compression (not hex... outdoor style, even if indoor) crimps on the ends of the cable, if you do not have the tools.