To add 'will' use the future tense: come arriverai / arriverate (singular / plural). Native speakers wouldn't say "arrive at", rather "get to" as per Duo.
You clearly wanted one verb but stuck two together: come sei arrivi = "how are you do you arrive".
Your suggestion accidentally means something else: either "same as/just like ..." or more likely "as many as..." "...six arrivals at the stadium".
Agreed. I played this on slow a half-dozen times, and I would have sworn the word was "staglio" - which makes absolutely no sense. But when one is being introduced to new vocabulary in the language one is learning - this is possible. However, I am well acquainted with "stadio" and that is NOT what the recording was "saying".