These revenues are NOT "best case". These are typical revenues that you can expect to make if you follow my 3 simple steps. Many people do much better that this – exceeding $10k per month within their first 12 months.
And remember, FanBox is not a place to "get rich quick". You're building a business – which means working hard, and incurring costs towards building your business – although almost all those costs can be paid using your FanBox earnings!