It's probably low because something about your file is making them nervous. It's a borderline approval.
No, the instant card number would have no bearing on the SL. That's entirely dependent on your credit report.
BTW it's expected you can't ask for a CLI when you JUST opened the account - the earliest you could possibly try is 3-6 months.
Congrats on your Amex BCP approval.
Congratulations on your Amex BCP approval!
Your account is just way too new to ask for a CLI. Congrats on the approval though.