I think foreign alliances would be important for the CSA in terms of having a country to help them industrialize, loan them money, and for them to base their military off of. The US could arguably be said to have never left the British financial sphere, I can see the CSA being in bed with French bankers and in love with the French military ideal until Napoleon III is gone and the Second Empire of Mexico falls, by which time the German military and industrial model would probably be looking very good.
There might also be more potential for Latin American allies than the bluster of the firebreathers over a Tropical Empire might suggest. Considering the CSA's existence alone provokes the United States, being able to challenge US hegemony in the Americas would look more like it would lead to stalemate than to triggering a conflict that could already be triggered by any number of border incidents. Also, control of Florida means lots of potential deepwater ports for European ships and in convenient range of the Caribbean.
Back on the subject of Germany, the German model is more accessible to the Confederacy potentially than you imagine: Belief in superior Protestant work-ethic and a highly federalized national structure with sovereign kingdoms/states making up a larger union (considering the Great War era German army still was made up of the armies of the major German kingdoms, that's translatable to the states-rights heavy CSA constitution, isn't it?).
The Confederacy could be Germany's route to challenging American industry for Latin American markets and challenging the British navy for control of the Caribbean. It wouldn't take a massive tropical empire, just a Miami-like port to be constructed in Florida and the probable possession of Cuba.