1.) A lot of the Landmarks are basically "do this specific thing, get 2VP for it six times". Did you every try those with 1 or 3VP?
The ones that take the VP from the card were always 2 VP (some gave different amounts not-from-the-card, like the Colonnade example or Tomb). Being consistent like that helps you learn the cards. It ends up easy on the components too, we included 2 VP tokens and you just put those on the card and don't make change as often.
2.) Messenger seems like the perfect replacement for Woodcutter and Chancellor, yet you said that you started working on the second edition after Adventures was released. Did the card infuence your decision to get rid of the old ones?
No. It had been clear for some years that Chancellor was too confusing and weak, and I had already one-upped it with Scavenger. And Woodcutter only left because I could put something more interesting in.
3.) There hasn't been a draw to X card in quite a while, what's up with that? Do you consider that mechanic more of an exotic variant to regular draw instead of a basic game mechanic? It saddens me a little that draw to X engines are pretty rare, they're so much fun.
There's nothing up. I think "draw up to X" is fine, and try it sometimes. There was one in Adventures; it didn't survive because it wasn't good enough, Artificer had nothing to do with it (sorawotobu), and Villa wouldn't have stopped one from being in Empires, there just wasn't one.
4.) Do you consider Travellers to have an Adventures flavour or could they fit into any expansion?
The mechanic could reappear, but it takes a lot of cards, and most sets wouldn't be happy giving up the slots.
5.) The japanese community found out about forum/trader/goons/cost reduction. This is a lot less complicated than the last infinite loop people were presenting, so it may actually come up in a game. If you had time machine, would you have worded anything differently to avoid that or is it too unimportant?
I don't know that I would change Trader just to kill the super-rare combo (your 4-item list leaves out "more copies of the cost reduction card" and for some of them "way to play the cost reduction card a bunch of times" and "way to draw enough cards to do this"). But I do think Trader is a mistake, and fixing it as it happens would kill the combo. I would either have no reaction at all (a sweet simple card that people would still use), or the reaction would be something like "When you gain a card other than Silver, you may reveal this from your hand, to trash that card. If you do, gain a Silver." The "would" part is super-confusing and bad. And as it happens creates an infinite combo.