Welcome.
I'm not really the right person to answer your questions. I use the altepg service but had no part in setting it up. Hopefully someone who did will read your post and respond but in the meantime here is what I know.
mirspace2000 wrote:Is there a specific topic or user I should contact to learn more about how this all works?
The Oz TiVo team in Australia did much of the heavy lifting and had Series 1 TiVo's working there long before TiVo themselves launched in Oz. Dave from tivoland knew them and they assisted greatly with the original UK efforts. tivoland has now closed but
http://www.tivoland.com/ is still there so the News from 2011 is worth a read.
Some basic user oriented info is in the FAQ here
viewtopic.php?f=8&t=670As far as how it all works under the bonnet
http://www.oztivo.net may have some useful info. I don't know how active the Oz TiVo team is now but the site seems to have some interesting bits and pieces.
mirspace2000 wrote:If one were to duplicate this for the US are there documents or information to assist?
I don't know I'm afraid - the oztivo site above might have some but I haven't looked in detail.
mirspace2000 wrote:I'm not even sure at this point if the altEPG service is free or a paid model. I'm sure at some point the modems and servers need to be paid by someone.
The altepg service is free (although donations are always welcome). The modems and servers are provided by some very kind sponsors who are TiVo enthusiasts. You'll find some names mentioned on the main
http://www.altepg.com page.