Also, when installing gentoo without an internet connection, then plugging in a cable connection after the install work? I'm assuming "yes".
If by this you mean "can I get gentoo networked after the install" then yes, of course you can. I assume you intend to do a stage three from the live cd if you have no network right? I just want to encourage you to do a stage 1 or 2 when you get it networked instead, because it will only install the newest versions of packages immediately.
With your method, you will be installing the old binary packages from the old livecd, and when you do your first "emerge -u world" it will take almost as long as a fresh source install anyway...
In any event, if you are stuck without Internet then I guess that's what you need to do...