Also, any pointers on dealing with the Muscovy-Ottomans unholy alliance, other than 'ally every other major power in Europe?' Considering they have the number 1 and 2 army sizes respectively (I myself am number 3)
Wait until AdmEff3.
Horrible advice, but without getting any screenshots or similar to go into detail this is the only idea I have.
You want to hit them hard with your first war because it will be resource-intensive as hell.
Both have brutal amounts of MP, high FL, Ottos probably have Quantity (Musc too sometimes) and the sheer amount of provinces you'd have to siege down is enough to keep you busy way beyond the CfP hits.
First war with AE3, seperate peace Mus and only force them to annul treaties with Ottos. Don't worry about other alliances, every other nation should hate them at this point (provinces of interest). Don't care about the strategic value of provinces to take, just split up Ottos where you think it'll prove valuable.
AI gets hit hard by these maneuvers and if you want to take the extra step you can plaster your new provinces with forts and comfortably siege down whatever is on your half in the next one. Ottos upgrade later than other nations.
Make sure you split them in a way so no troops will get created or positioned on your side.
Example: Early game you want to split at the straight. The later it gets, the more eastward you will move. Just as a rule of thumb.
As for how to deal with them during their first war: You're at the AE3 point. Both have fallen off due to their bad scaling. You need at least offensive and a second mil tech. Anything below that will get complicated.
Unless you're a colonizer. In that case you just grab NA+SA with the usual route, get up to 1-2k income and throw mercs into their face to no end.
Did it as Castille once out of boredom. 90 units over my FL, permanent merc limit and consolidation whenever a stack was fleeing, took about 3 months per province.
WW1 in Anatolia, I guess.