Raspberry Pi + Tor

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Hi guys!
I just buy from your shop my RaspberryPi.

Very love your article here:
https://learn.adafruit.com/onion-pi/overview

SO, I want do that.

BUT..
What I need to do (how setup?) if I don't want use Wi-Fi for getaway of Tor?I want to use the Ethernet for Tor getaway. Could you mind help me with this issue? Also firewall is very important for me (don't want my traffic passed tor!).
I ask because I absolutely don't understand Linux and did everything step by step like in article.
Need your help. Thank you.

Sorry for my bad english.

Thanks.

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I forgot to say that the Internet is via a USB 3g modem (how I can setup it?)

Thanks a lot.