My vote would be to start a new tread named something like "House for sale in (area)/Germany - BTC auction" and link to this tread in the OP.
If possible it might only be open for posts by users who first made contact via PM.
there is a function that allows you to do that?
I do not know, hence the "If possible", but I know for sure that it's possible to make a trad where OP is moderating it. Not quite the same, but you could remove any clutterposts.