Was there a steady progression of technological development (such as metallurgy) that had to be completed in order for other key inventions (such as the movable type printing press) to be created?
Was it more a matter of no nations of the medieval era having the time and resources to spend on things other than survival and warfare?
I know the arrival of Byzantine scholars in western Europe following the fall of Constantinople to the Ottomans played a role, but I get the impression that their contribution was to bring in their library classical knowledge, which could (hypothetically) have been done at any time had the circumstances warranted it.
This topic is very complex, as so many aspects of when, precisely, the renaissance started are debatable, and the renaissance started at different times in different places, with different influences in each location, and the results show; the 15th century in Venice was much different than the 15th century in Florence. I could talk about the republican governments of early Italian city-states, the population density in northern Italy, the comparative isolation from high medieval warfare that Northern italy benefitted from, the early breakdown of the feudal system in Northern Italy, as well factors unique to each center of the renaissance, each with their own causes and influences. Was the Renaissance really a "Rediscovery" of ancient knowledge, or was it simply an artistic movement brought about by progress and economic prosperity, which spread from Florence to Italy, and then across europe? Does it even have a start date?
Good old John Julius Norwich states that the Venetian renaissance starts precisely in the year 1400, the year of the completion of the new Doge's Palace. But Petrarch states that everything, him included, that came before him belonged to a "Dark Age". Is he taking credit for single-handedly starting the renaissance in 1342? Renaissance historians, looking back, declared their generation the harbingers of a "New Age", and used Petrarch as a starting point. But starting point of what? Petrarch was a Tuscan who lived in Padua. Did he influence the Venetian renaissance? Was he a product of the Tuscan renaissance? Was he both? Or is something wrong here?
Baronius, writing in what would be termed the late renaissance (and the counter-reformation), said the Dark Ages lasted from the fragmentation of the Carolingian Empire to the gregorian reforms in the 11th century. And he might not be half wrong; what about the "Renaissance of the year 1000"? And the earlier Ottonian renaissance in Germany? What about the 12th century revival of scholarship and the foundation of the University of Bologna?
Then again, I was taught in middle school that the Renaissance started in 1492. Should the renaissance start when the early modern nation states catch up, culturally and economically, with Northern Italy?
The construct of the Renaissance is really rather limiting, and much of the most cited scholarship on the era is hopelessly outdated; Michelet, Mommsen, and going all the way back to Bruno. Another user on this sub proposed that the Renaissance for a whole is due for a revision. And he's completely right.
The origins of the renaissance are in the Dark Ages, as flawed as that concept is. They are disparate and complex. You might find the answers to your question in a book called, Barbarians to Angels: The Dark Ages Reconsidered by Peter S. Wells (W. W. Norton, 2008).