Do you think the blockcypher.com can give a accurate estimate fee? well i check the site and saw that the 3rd one is the lowest which is 0.00076 BTC/KB
Do you think if we set the fee on electrum you will pay for exact amount of 0.00076 every transaction if you set it or it will determine the transaction size first?
For Electrum, if you choose dynamic fee, the client factors in the network load and the transaction size. If you go to preference, you can also choose a fixed fee or manual fee. If you choose fixed fee, the transaction is paid according to the transaction size and your fee that you set. If you use manual fee, you can put the fee, regardless of the transaction size.
Personally, I'll just go with Electrum's dynamic fee. It is quite accurate with the estimation and its pointless to go to other sites and manually input your fee.