1. Before deciding on your starting class, I think it's best to decide what Soul Level you want your character to reach and what your important stats will be at that level. After doing that, you can decide which class has starting stats with no points allocated wastefully.
2. This is pretty open to lore/roleplaying interpretation. I guess you might want to kill everyone aligned with Gwyn, since they warred against the ancient dragons. Priscilla is an interesting case, since she's a partial descendant of the dragons, so depending on how you interpret that, you may want to spare her or eradicate her.
3. Some Dragon-oriented ideas: Dragon Bone Fist, Dragon Greatsword, Dragon King Greataxe, Dragon Bone Tooth, and most fire Pyromancy in general.