Between LABITCONF and Devconnect Buenos Aires, I've helped run events for tens of thousands of people combined. A few things held true at every scale.
The event is won or lost in the coordination layer, not the content. Great speakers and a great venue are table stakes. What actually breaks or makes an event is whether the fifty small decisions happening simultaneously, badge printing, press credentials, a delayed flight, get resolved without anyone in the audience noticing.
Sponsors remember how they were treated more than how big the stage was. The relationship that gets renewed is the one where someone answered the phone at 11pm the night before, not the one with the fanciest booth.
Press coverage during the event needs its own team, separate from operations. Trying to run logistics and real time media coverage with the same people means both suffer at the exact moment they matter most.
And the growth from one edition to the next never comes from a bigger marketing budget. It comes from the last edition being genuinely good enough that people who weren't there heard about it from someone who was.