@Kartongen - First advice for anything mod/taint-related questions would be to PM a mod. I will 100% guarantee that the mods (and forum, but ESPECIALLY mods,) would prefer to tidy up any possible confusion of taint and non-FAM before having to send out PM's to half the MP/trade community requesting people to delete items/characters and issuing bans. In addition, I am sure it's somewhere in the rules, but a Mod would be more than happy to direct you in the right direction, rather than chase things up later.
There isn't really a thread specifically for small/quick questions, although several have popped up over the years, and generally disappear after a while, before a new one pops up or an old one is revived. EMB is a place for a chat and small questions, but mostly off-topic general spam/chat, while D2 lounge is another possible place, but both aren't designed for your type of question.
A new thread to provide full disclosure to the forumites and mods discussing your decision and asking questions is also more than acceptable. In this, if your friend is happy to do so, (s)he could happily introduce themselves as well, and share their opinions/experience and background for D2.
My personal advice is to try get the friend to join the forums a little bit, create trade profiles, and be a (semi-) active member. Maybe you can get a few others with similar times to join in your MP as well. Other than that, isolate off-forum items/characters. Either start a new character, or simply have a gomule stash specifically for MP with this off-forum interaction, and consider that everything may (or is) potentially tainted by something the forum doesn't want. And only trade MP on the forums with items/characters that haven't interacted with someone else who is not part of the forums.
Congrats as well on leading Vahana to defeating the evils of Sanctuary!
Yeah... *reluctantly joins the toast to Vahana*
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