I recall you need to pay a fee when moving out of coinbase, not sure if that was still a thing since I never used coinbased when they had added a transaction fee. But basically you are doing a good job. Poloniex has one of the lowest fees right now to withdraw from the exchange, however, they might flag you though if you do not really trade and just use it for a wallet. Not to mention you are withdrawing and depositing from gambling sites. This could trigger AML policies.