Yea blockchain.info is definitely a solid wallet, i think its safe to use it up to 10 bitcoin.
After that you need offline vault.
No, it's not. Blockchain.info is not a secure online wallet. Now, the only secure wallet which I can think of is GreenAddress. Blockchain.info seriously flawed. It may have been a secure online wallet earlier but not now.
are my wallet is secure ?
i use blockchain, i back up it and i restore to electrum wallet ( android) ?
After you import addresses, I suggest you to delete addresses from your Blockchain.info wallet and then I think you are secure. However, I recommend you to send all Bitcoins to new address generated in your wallet, here, Electrum.
By the way, does Electrum android support importing address?