Storage data is stored on the server by different encryption methods .. some of the best ...
Doesn't matter. It doesn't mean that you can't steal the wallet and run away. How are you going to use the coins if you don't have to decrypt it at some point?
It is possible to send a transaction with the fee you want with some wallets (at least blockchain.info has this option) but the fact that you will send it doesn't mean it will get confirmed. The problem is that it might be even returned back to your wallet if it doesn't get confirmed for a really long time.
Nearly all the wallets allow their user to choose whatever fee that they want.
this is too sketchy. can you make it open source?
It doesn't matter to. You can't verify the code that the site is using. I can throw out a clean code and put a malicious code on my website instead.
I can guarantee that this is a scam. You can make the fees lower if you send to many different addresses in a transaction, gathering all the transactions and sending them using one input and many outputs. This decreases the privacy of the transaction and requires a huge trust on the wallet provider since they will essentially be controlling all the coins.
Tl;dr: This is a scam.