Is this necessary to send my all bitcoins to my new electrum wallet or any other BTC address like blockchain or any exchange.
Yes, you can skip this part.It's not a mandatory step. But it's recommended to avoid replay attacks.
If you don't want to, you can simple import your wallet in Electron Cash and use both softwares to manage your coins on both chains.
And How to import my old wallet (containing BCC and no Bitcoins) to Electron Cash.
Electron Cash has the same interface as Electrum. Just follow the steps when you open the software and import your wallet with your seed phrase.