Near perfect IVs are required in competitive. Perfect is expected. Charizard is suitable and allowed in OU. As for any other questions about tiers, you can just search Smogon.
I don't know if you're new to Gen 6 competitive, but if so then you've got a lot to catch up on before Gen 6 OU competitive if you haven't done Gen 6 competitive before. A lot has changed since Gen 5. There are a lot of good Megas in OU, and with them comes new battle dynamics and expectations.