If conquer at hall of legends and pay 1 to ready my Azir legend, do I need to play a second gear or have I met the requirement by already playing one gear this turn?

Yes, you've met the requirement. Azir's ability says "Use only if you've played an Equipment this turn" — that checks the entire turn up to the moment you activate it, not just what happens after the legend readies. If you played a gear at any point this turn, the condition is satisfied.

This is distinct from the Ornn's Forge FAQ (#411), which dealt with a forward-looking "your next gear costs less" effect that couldn't look backward. Azir's condition is the opposite — it looks backward at what's already happened this turn. You don't need to play a second gear.