Do I draw cards or reveal Battlefueled first?
According to the standard Start of Game procedure, you determine your Battlefields before you draw your opening hand.
The sequence is as follows:
- Reveal Legends
- Choose Champions
- Determine Battlefields
- Decide Play Order
- Resolve Mulligans (which involves drawing your opening hand of 4 cards)
- Start the Game
As noted in the RiftJudge FAQs (specifically FAQ #7149 and #3373), battlefields are revealed and selected before determining turn order and resolving mulligans. You draw your opening hand of 4 cards as part of the setup process (Rule 116), which occurs after the battlefields have been established.