In addition to the multiple unit build queue hotkeys I suggested earlier in this thread, I would also suggest another minor interface improvement which is to display the total number of troops currently selected when you selected more than one armies in the field. Suppose you might deploy those field armies along the border of a country you're gonna declare a war upon, you might want to know the total number of troops you have currently deployed along that border, especially if it's a large number of field armies that would take time to count all, and compare it against the potential number of enemy troops you might face in that upcoming war (obtained via ledger although this probably should be only obtainable via espionage). You already can find out total number of troops for your nation but you might want to know how many troops you have at immediate disposal in that area, not all troops that might be dispersed all over the world.
In my case, I have a large number of troops currently deployed on territory of an allied state in Germany region ready for a war against a Great Power that need to be checked in its expansion in Europe, currently waiting for an opportunity to strike (no CB at this point yet) and my national army are organized into field armies I labeled "divisions", each consisting of 15,000, rarely more than that. I don't organize them into larger units as so to make it more flexible, allowing transfer of troops to where it is needed. At this point, I have like 18 divisions or more, so this is sort of hard to count immediately when I had to add them up. Anyway, just a minor suggestion, not an absolute necessity.
Also, on an unrelated note regarding no CB situation against a Great Power I felt to be unduly large and thus threatening to the balance of power in Europe, I think there should be some kind of "Balance of Power" casus belli somehow, designed to enable some countries not interested in territorial expansion within Europe but want to maintain balance of power to accomplish that objective. In my case, Austria is in PU with Prussia and has large territories, already beating up on France, which in my opinion make it a threat to balance of power. It's impossible in my case though to make alliance with France or Castille. What made it worse, though, is that it's allied with Sweden (which controls Norway) and Russia. So I'm facing really a big number of soldiers in potential conflict with Austria. I only have for major powers Portugal and Byzantine Empire to rely on. Yet I can't do anything about it unless I want to take -2 stab hit and declare war on Austria. Might have to do that, though, or I might face Austria with more ports and bigger navy to contend with. Hmm, some thinking to do here.