Hi Nigel,
A product weight is required to display the Ship To, and Shipping Method fields on the Cart page as a product with a weight of "0" technically will not need to be shipped and therefore would not need select a Shipping Method.
Regarding your inquiry, the ability to restrict Shipping and checking out depending on the Country selected when using the Shipping by Order Amount method isn't currently supported. As a possible solution, you could use the "Zone Shipping By Quantity" or "Zone Shipping By Weight" methods which will allow you to define Shipping Zones and the fees associated.
We are also available to program the ability to restrict Shipping and checking out depending on the Country selected when using the Shipping by Order Amount method. I will also move this post to our Enhancement Requests forum to give others a chance to request this as well.
If you would like to team-up with another user, or your company has budget to sponsor this feature enhancement let us know, in most cases we can start work on the new feature within a week.
If you would like to prioritize a feature request to the top of the list do one of the following:
Submit a quote request here
http://www.smith-consulting.com/servi...
Email
sales@smith-consulting.com
Please let me know if you have any questions.