I would like to build a long range (10s of kms) wireless link in the unlicensed spectrum (like amateur radio - maybe 27 MHz, ideally with variable frequency setting). The transfer speed requirement is at least 1kB/s (9600 bps). I have no experience with HAM radio or packet modems (TNCs etc.).
It seems you are going to build some sort of packet radio system on CB-frequencies. I think it is perfectly legal in many countries, although you should consider local laws.9600 bps is not easy to get at distances you are thinking, but it is not impossible. Depending of terrain you might need quite tall antennas.
If you are going to send/receive email, pictures, or other "human data" you could consider some other options like PskMail or Fldigi -software, both usable at raspberry.
Take a look of this example: http://kissactiongroup.wikispaces.com/PImp it is my project in amateur freqs, but principle should works on CB also.
If you are going to take your idea further, I hope you contact me via my facebook profile. There is also another radio amateur who is currently working with Pi/datamode over radio-subject. Also you can contact us by joining this FB-group:https://www.facebook.com/groups/1519431578386685/ (do not worry about language...)