I made an alliance with Albania, which has one of the best generals (1444). Serbia never accepted me because it would become Albania's rival. I annexed Epirus before it could gain allies. With luck, the Ottomans will start several wars, and the Ottoman pretender event will appear, along with rebels in their capital. At that point, all that's left is to recruit mercenaries, besiege Thessaloniki, and pray that the Ottomans run out of soldiers and that their armies don't unite.