Except that both Nicholas I and Alexander II were extremely cautious men when it came to foreign policy. You're not very likely to get a more 'aggressive' Russia ITTL with either at them at the helm in St. Petersburg, and certainly not one interested in even attempting to push the Turks completely out of the Balkans utilizing revolutionary nationalists.
Nicolas I was not a supporter of revolutions, but he saw himself, and his country as the protector of the Orthodox flock. To that end, he was willing to support revolutions so long as they did not oppose "legitimate" monarchs, and the Sultan and Caliph was not one of them in his book. He had already stripped the Sultan of nearly half his Balkan territories when he gained suzerainty over Wallachia and Moldavia in 1829
At the beginning of his reign he had supported the Greek revolution against the Ottomans. Now, Greece obviously held a special place in his heart, but in practice he saw the Bulgarians and Serbs in the same light: oppressed Christians who properly belonged under his protection. In Nicolas' mind booting the Ottomans out of the Balkans was not so much a revolutionary action as a re-establishment of the natural order of things as he saw it.
Now, to gain Austrian support Nicolas would have to make some compromises, probably along the lines of making the Principality of Serbia a protectorate of Austria, granting Austria Bosnia, and possibly expanding the borders of Hungary a bit. In exchange for such concessions, Nicolas would seek to establish a larger Greece, a subordinate Kingdom of Bulgaria, and independant, though subordinate kingdoms of Moldavia and Wallachia at the very least.
What this conversation has been ignoring, however, was that Nicolas began what would become the Crimean War under the assumption that it would be a limited war against the Ottoman Empire after he believed he had gained tacit British acceptance for his actions. You are correct about his caution, if Nicolas had understood that his actions would entail a general war, he probably would not have taken the steps that led to war with the Ottoman Empire.
But if Nicolas had believed from the start that his conflict with the Ottoman Empire would entail war with Britain and France, and decided somewhat against his personality to proceed regardless, he probably would have adopted a more aggressive posture, since there would be no point in restraint in the Great Powers were going to be at war against him regardless. He also might have engaged in a some serious diplomacy with Austria, rather than assuming that Franz Joseph "Had" to support him for reasons of honor.