But there wasn't any problem with it being available to level 9 characters, where the Breen series is far beyond?

Also, what specifically ties the Breen series into "The 2800". I can't remember any specific dialogue, but then again, it's been over 6 weeks since I read the Deferi's responses.

If it's just the fact he's there, don't forget you meet him on K-7 for the diplomacy mission, so it's not that.