No minimum required, although the staking fee is currently 0.18 BCO. So if you have 1 BCO, you will lose 18% to the staking fee. If you have 10 BCO, you will only lose 1.8% to the staking fee. So it's better to stake as much as possible, so that the fee represent a smaller portion of you stake amount.

There is an online calculator to help you investigate your possible return, 50 BCO could still be worth it. If CB takes off, and there's every chance it will, then at the very least that 50 BCO will be worth a lot, lot more one day - as well as providing you with passive income.

https://cryptobridgestakingcalculator.com/