Looking at this from here, assuming it is initially released with 25 episodes (though there may be more), the anime will most likely cover the Mercphobia Arc, and the Aldoron Arc. The former is only 23 chapters long (and that's counting the first couple intro chapters), and since they can't drag an entire chapter across one episode, I think they could cover it in twelve episodes at the most. The second half will then be devoted to the Aldoron arc, and it'll end there (probably with Selene), presumably to await for the next season. There is always a possibility to bring it down to less, though (for a little perspective, the Phantom Lord arc has 23 chapters, and only 9 episodes; the Tower of Heaven arc had 28 chapters and 8 chapters; and the Alvarez arc had 108 chapters, and 44 episodes), and squeeze the Elentir arc in as well.
Now, that's obviously not accounting for potential filler episodes, or expanded scenes, though the more I think about it, the more I'm willing to guess that the show may not need it, if it is going to be released on a seasonal basis. That said, while I don't think it's likely, it is possible that the producers will put pressure to have the manga released at a quicker pace, so that they can keep the series going, and not have extended breaks.
(YES, I am really overanalyzing this; NO, I am not sorry XD)