"5. If three or more teams are tied for #1, the #1 team is determined by tiebreak, the tiebreaker is restarted for the remaining tied teams, and that new tiebreaker for the remaining teams comes down to step (c) — the record against teams in the standings top-down — does record against the #1 team matter?

In this case, I believe it does not.

Step (c) states "When arriving at another group of tied teams while comparing records, use each team’s win percentage against the collective tied teams as a group (prior to that group’s own tie-breaking procedure) rather than the performance against individual tied teams."

Between my prior answer that excludes the current group of tied teams and this clause which states that the comparison is prior to other tiebreakers, I believe your record against teams tied with you is excluded even if that tie has been previously broken.

I cannot guarantee this is how the Big 12 interprets their own procedure, however. This is another case where the new, improved Big 12 tiebreak procedure is too vague."