If you want to withdraw STORJ to exchange, you need STORJ address from Kraken, bcs Coinbase doesnt have STORJ.Simply change your adress to that from Kraken STORJ wallet address
There is no problem using Metamask.It is a trusted service.Just connect Myetherwallet with Metamask.Then activate Zksync with your Metamask and you are good to go.
Look at here for info