Destroyers are of too limited use for the 12 IPCs you spent on it. If you build nothing for the Baltic, you should immediately run it away because it does nothing for you where it stands, and pray it survives or takes out lots of airforce on its way out.
If you do build something for the Baltic, good things to try are one carrier or 2 tran, and also try linking the navy by sending the med fleet west on G1 (use bid to take out Africa). Linking may not be the best way to go, but you need to practice it and understand how to use it and how to counter it, or you will be surprised by it.
Simply defending the Baltic with a carrier isn’t too helpful either, the Allies can simply bottle you up there with combined defenses until the US fields enough fig to disable it.
I remain pretty unclear on the whole matter of whether or not it’s worth building navy with the Germans. It seems to be very give or take if the Allies know the correct response to all the naval situations. If they don’t know the counters to the German navy/link, you can score some cheap wins that way, but when they wisen up, it’s not that difficult because it lets Africa go back to the Allies with little effort.
But if you build no navy, it just means the Allies get their shipping in gear faster, and you have more land forces as well, so it’s not like you get a clear advantage in either situation. Build one carrier + link, and the Allies will be screwing around for a round or 2 with your navy, but they get Africa and you have 5 less inf to defend/push.