I don't have the answers to all your questions to i can give a reply to what i do know/think: to your first question as far as i can tell there has never been a specific level to start pvp from. Second since your a level 73 balance i would recommend you use the hood of judgement, boots of judgement, House of scales raiment then bear claw of balance and the golden ring of battle. This as much as i can provide i hope someone else can help you out with a deck set up and strategies.
A pet that I would recomend could be a minion summon pet with double resist and triple damage or a pet with certain popular pvp school wards. If you want critical you could possible replace a damage or resist with a critical talent.
