Most of Europe is off limits. Too populated, to far away from their power base, and too strong to digest. I mean at best you can get Italy, but that's a very hard pill to swallow. Rest of the world is easier.
This can be done if you have Osman II survive and eliminate the Janissaries (and other slave soldiers such as the Mamluks). With this it will be much easier to fix the structural problems and mismanagement of the provinces as well as implementing the needed reforms to keep pace with Europe. Basically, a Tanzimat 2 centuries earlier, with the added caveat of having Egypt be fully integrated, rather than a 'state within a state'.
I believe it'd be easiest for the Ottomans to expand in Africa. They could, should there be a scramble for Africa expand across most of the eastern Sahara and Sahel. OTL the Egyptians captured Sudan and even bits of northern Uganda and the Ottomans had influence around Eritrea. Here they can take that, perhaps have influence over the Great Lakes states (why would they want to rule them I have no idea), Bornu and the Sahelian states of Northern Nigeria.
Following that, the Ottomans could take more of Persia, the Gulf and the Caucus- Azerbaijan, Georgia, Basra, the Gulf states; perhaps even Oman.
This is of course being extremely optimistic.