Might want to think about a couple of cities in multiple regions around the world, rather than trying to complete a country as tourist typically season varies per region. For example, Africa (Cape Town [SA]) and Oceania (Sydney [AU], Brisbane [AU], Bali [Indonesia], Auckland [NZ], Suva [Fiji], Noumea [New Caledonia], Port Vila [Vanuatu]).
Will add Tbilisi to top of the list for the next cities we add as well.