*jDip.
I got to 24 SCs in 1903. Not sure if my route was optimal or not. Russia starts with 4 SCs, and going to 8 is easy. That leaves you 8 units; I went to 14 SCs but only had 12 units with which to work. Those 12 netted me 10 more for a total of 24 in 1903. I ended up taking Edinburgh, Germany, Scandinavia, Russia, Austria-Hungary, the Balkans, Turkey, and Italy; the Lowlands, France, Iberia, Tunisia, Liverpool and London were left standing.
Draugnar's correct. Russia hypothetically could field enough units to net 28 SCs by 1903, but it can't field them in the right places. You need too many armies in the East to make it to Italy by 1903 without missing any of them; subsequently you can secure Germany but can't get beyond that.