If the Holy League fleet had been annihilated at Lepanto, would the Ottomans have been in a position to capture Brindisi or Otranto that fall, or land an army on the heel of Italy next campaigning season? What kind of opposition would the Spanish and their Italian allies be able to offer, and on what timetable?
What could happen: the Ottomans could capture Brindisi and Otranto. It happened as late as the early mid 17th century. But here is the catch. An invasion of Italy is hard around 1571. Why? For one the Spanish are in an excellent position to defend against an invasion. The Ottomans still have to deal with the Austrian Habsburgs in Hungary if they felt attracted enough to invade.
There is some help though: The Dutch Revolt. There is 6 months between the Battle of Lepanto and the Fall of Brielle which led to the worsening of the Dutch Revolt for the Spanish. The possibilities are that Philips II is bankrupt again and so has only a little choice now between the Lowland and the Kingdom of Naples and Sicily. He can go for both with the risk of losing both though. Considering the Ottomans won in Lepanto it means that Venice will try to end the war ASAP to lose the minimum (Because I rather see the Ottomans invade Crete than Italy after Lepanto IF Venice continues). Spain, the Knights, Papal States are left to fend off a possible invasion.
How would a succesful invasion look like? It might look like this: Ottoman-Safavid War of 1578-1590. In theory succesful, largescale conquests, in this case in Southern Italy and possibly Rome. But with the result of weaking the Janissary Corps, overtaxing and thus causing rebellions in Anatolia. And It will take some time to beat the enemies. However... I find it unlikely. Too much costs. The Conquest of Western Persia, Azerbaijan and the Caucasus were held for only 30 years or so and dealing with large rebellions until the 1650s. Not really worth it.
What I would expect: conquest of Malta, Corfu or Crete and maybe Sicily (in a campaign of 5-12 years). Conquest of settlements on the coast only to be abandoned later.
I hope you got your answers
