I believe you can achieve the sequence number functionality in the webquerysave event of the form. by taking hold of the latest document by getentrybykey(year(now)&countryname).
If your application is on multiple servers, you have to take into account the possibility that multiple docs are being created relatively simultaneously on the different servers, and thus might get the same sequence number.
Even if on only one server, it’s possible to have this happen if the docs are created within some short time interval (1 second?) of each other. So it depends how important it is not to have any dupes.
You can have an agent run at night to clean up, but if it’s important to get your sequence number Right Now when you save the doc, then that’s harder. But yes, just have some view that holds these docs in an appropriate order and grab the top/bottom doc.