Was Baratheon the house name of the last Storm King?
NO. Baratheon is Orys' surname.
Where was Lord Rickard when the news arrived that Brandon had raced off to King's Landing?
GRRM did not say. He gave us very little information on this.
5) Is there a Lord Selmy, or are they just landed knights?
They are landed knights. Would not go into detail.
Arya WILL be in Feast. I asked GRRM specifically and he said, yes.