I have a doubt. Is Coinbase to coinbase transaction free? Whats the minimum amount in btc that can be transacted from one coinbase account to another?
As far as I know, transactions taking place between two coinbase account and wallets does not incur any network fee. You have to pay miner fee if you making transactions to an external wallet. You probably can't change the fee (never bothered to check 
).There is no fixed minimum amount of BTC that you can transact from one coinbase account to another.