I'm definitely not an expert, I only started doing BD during the Wraith Resurgence event. Some of the weapons I use aren't buyable I believe, as they're from that plot.
But my main used weapons that are buyable are Yooyu Knuckle Duster and Turned Tooth. I also have Patched Magic Hat and Greater Healing Scroll but to be honest I don't use them really.
My battle pet's stats aren't super super high. She's level 74 at the moment. I recommend getting to at least level 50 because then you can train a really valuable battledome ability that completely blocks the enemy's moves for one turn (the