I've been reading Reg Zzzzzzzzzzzzzz, oh, sorry, must have dozed off, but I'm awake now! 226.1(c)(2)states that certain provisions apply to business credit cards. Does this mean that all of Section 226.5a applies to business credit cards, or just Section 226.12?

Look at footnote 4 to 226.3 Exempt transactions. Only 226.12 (a) and (b) apply, issuance of credit cards and liability for unauthorized use. And (b) applies only if less than 10 cards are issued.