1)
What is the significance of Oholi'av ben Achisamach from the tribe of Dan, as Betzal'el's second in command (in spite of the fact that Dan was the lowliest of the tribes, whilst Betzal'el was from Yehudah, the leader of the tribes)?
1.
Rashi: It is in fulfillment of the Pasuk in Iyov, 34:19 " ... nor is a nobleman given recognition over a pauper.