1)
Does the goat represent just one king?
1.
Malbim: It is Malchus Yavan.
2)
Who was the first king [discussed here]?
1.
Rashi: It is Alexandrus Mukdon, who killed Daryavesh ben Esther, like it says in Sefer Yosifun. Malbim ? there were kings of Yavan before him, just he was the first king of Yavan to rule over the world.
