1)
Why were they Shochet the bulls first?
1.
Malbim: Normally, Dam Chatas precedes Dam Olah. For Helam Davar [of idolatry], the Olah precedes the Chatas. Along with the bulls 1 , also the rams [and lambs], which were purely Nedavah, preceded the Chata'os.
1
Refer to 29:21:1:1*.
