1) Which wallet should I choose to keep btc? There are so many choices so that confuse me. I know about Electrum, Blockchain, Coinbase,... Does it secure?
1) Coinbase = centralized just like paypal so better not to use it
Blockchain = client side encryption so storing small amount of bitcoin for daily use is good.
Electrum = desktop wallet which is quite secure than web wallets
I suggest you to use paper or hardware wallet like trezor if you want to store large amount of bitcoin.