I would be more worried about getting some obscure team from the edges of the continent than Dortmund, we do better against the bigger teams. Besides, we're in pole position for third place anyway.
That's unlikely, the way the playoff round is organised in the last few years. On the one hand there are 5 ties for 10 league champions of "lesser" leagues ("Champions route"), while on the other, there are 5 ties for 10 placed teams in bigger leagues ("League route").
Last year (don't know how the national coefficient have changed for next season), the "League route" teams were from England, Spain, Portugal, Netherlands, Germany (seeded) and Italy, Romania, France, Switzerland, Russia (unseeded). If we were to be 4th and unseeded, which is well possible despite our EL run last year, we'd be all but guaranteed a quite difficult tie.
http://www.uefa.com/uefachampionsleague/news/newsid=2394111.html