I think No.1 above is probably my only option at the moment. Keep the free version out there and then come back to the issue in 6 or 12 months to see if anything’s changed.
The lack of any meaningful usage statistics for CP doesn’t help matters.
Unfortunately No.4 isn’t an option for me. Forms plugins generally support Stripe and PayPal, that’s it. Stripe isn’t available in my country and PayPal has let me down seriously (financial loss) in the past. So when I need to accept credit cards, it will probably be Braintree, which means full blown e-commerce.