About forums being echo chambers: it's true that taking the advice of random users on a forum is as risky as taking the advice of a seller. The advantage here is you can take some time to read other people's posts and see for yourself whether they're knowledgeable or not.
I'm afraid I can't offer you any real advice, as the Yixing world is pretty much new to me as well. I can however recommend this flowchart from Steanze on the different types of clay: viewtopic.php?f=19&t=318
. Should help clearing some doubts along the way.
, always copy your posts before submitting them. AFAIK most forums are still designed to refresh after a while.