I'm aware that Cuba was in many ways an agent of Soviet interests, but I'm also aware that Cuba had its own political ideals and sometimes clashed with Soviet control.
Now add to that the relatively small geographic area, population, and economy of Cuba, and contrast it with the breadth of its foreign influence during the Cold War: military actions in Angola and other African nations, diplomatic presence in Oceania, military and economic support throughout Central America. How did such a small nation have such a large presence?
Was Cuba purely a pass-through of Soviet influence in these far-reaching influences? Or was Cuba able to self-fund these efforts through domestic economic activity?
I wrote this answer on the very connected topic of Cuban medical diplomacy (though not the military missions) with one focus on Angola. One additional point for your question: medical diplomacy was very cost effective for Cuba in that training doctors and carrying out those specific operations are comparatively not that expensive, but bring many diplomatic advantages as I discuss there.
Hope this helps!