Is there a minimum for the 3 outputs?
Yes. Three of your outputs are 0.001 mBTC, which is equivalent to 100 satoshi. As BitCryptex has said above, the minimum output you can send is 0.00546 mBTC, or 546 satoshi. You either need to remove those 3 dust outputs from your transaction, leaving only the one for 6.21 mBTC, or you need to increase the amount in each output to above the minimum of 0.00546 mBTC.
Sending the minimum amount to 3 different addresses will only cause you more problems further down the line when you try to send them on, as once you deduct the fee from the minimum amount you will again have too small an output to send. Sending to an intermediary address before the final destination also does next to nothing to anonymize your transactions. If you are trying to anonymize your coins, you would be far better off looking in to a mixer such as ChipMixer, or a CoinJoin transaction.
