Yeah, there's still a lot of basic empire management stuff you can learn more about.
Like when to build harbors, for instance. You've got some small islands that don't have a lot of land tiles to work. So your citizens are working water tiles, but are only picking up 1 food that way. Building a harbor makes that 2 food, and would allow those towns to grow again. Although some need an aqueduct to grow beyond size 6.
Another advantage of harbors is that they allow transportation of lux, so your island citizens will become happier as well, as they gain access to the silks. And you need to need to hook up those gems in your territory as well, of course.
As for the war against Russia, I would have claimed all that open space inbetween you and Russia first.