Adding a subscription needs to have more flexibility and not require you to create it, then go back and edit it to get the credit card associated with the subscription.

Flexibility: I should be able to select my begin date when the subscription is in the middle of a cycle (e.g. back-date).

If collecting payment offline (e.g., invoice customer), I should be able to select what dates I want the billing cycle to be like 20 days prior to due date while still being able to collect credit card payments on other customer on their subscription date.

Ease of entering data.... unless you check 'accept payment offline' the subscription data entry is not complete without a valid credit card associated with it.... the system should require that entry before accepting the subscription.