Hi,
Yes you can pay the difference of $27 and upgrade the license. You will need to contact our support team on [email protected] to do that.
It is possible to block checkout if the minimum amount is not met based on the shipping zones. There is an option under the General settings of the plugin to Block the Checkout Process. The user “Angel” had a different issue on minimum’s not being set up correctly which was resolved.
We have not tested the plugin with Order delivery date pro, but don’t see a reason why it should not work with it. As our plugin will limit the minimum purchase amount based on shipping zone and the Order delivery date plugin will limit based on time.