Hi Tom,
Thanks for getting in touch and for your interest in our products!
I’m not sure that I completely understand your first question- you can manually mark approve a payment on the backend of your site, but that’s generally for when users are paying with an offline method like a check. In that case, you’d mark the order Complete when you received the payment. If your user pays with Paypal or credit card, the purchase will be marked Complete when the payment is received.
The free base WooCommerce product does not come with MailChimp integration, but I checked out their site and it looks like they have a premium extension for it.
Best,
Leah