Successfully complete all of the training missions (every icon has three things under it) to unlock free play for arcade mode.
When playing with a Guncon, insert a standard controller in any of the other free slots. Rotate the Analog-stick repeatedly and listen to the reloads.
The silver earring is the best [only one player needs to equip it] since each barrel shot drops 100$ in pot. The holy earring is too holy to be helpful. You can conserve money by buying the silver badge first [sold items give 20% more money] before buying the members badge [items cost 10% less money] This helps when trying to buy expensive weapons like the 92.5 silver bullet.