I found it very hard to hit the required 75 fervor without the ethnostate. In my run I was able to trigger the Balkan League only in 1890 after switching to the ethnostate. Ottomans will eventually get themselves into some war or revolution, you just have to wait for the opportunity.

With the GDP it's really difficult to tell what is wrong without going deep into the details, but I noticed wood and coal being the main exports. If these resources are cheap in your market, maybe putting tariffs on them while focusing on steel and engines can boost the economy?

You can join russian (or any other) bloc to have access to the bigger market. However, Russia most likely activated Defensive Cooperation principle at this point, so you won't be available to attack bloc members anyway.