Ah, thanks HCP. I assumed they'd both work of the same software (although bip91 has been implemented to make both networks replay-proof).
It's probably a good idea to try to empty private keys before putting them into another software (especially if the developer isn't known - if ThomasV is not the producer of electrum cash).
Yes, definitely... it is even recommended by ThomasV in his post about Electrum and BCC:
BCC wallets will require you to import your seed or your private keys, which can be exported from Electrum. Doing so will expose all your Bitcoin funds associated with that seed to the BCC wallet you decide to use.
Therefore, *after* the BCC fork, but *before* you enter a seed or private key in a BCC wallet, you should move all your funds to a new Electrum wallet, with a new seed. You will still be able to use the old seed or private key with BCC, because BCC has replay protection. Wait until your funds are confirmed in your new Bitcoin wallet, before you enter the old private key in a BCC wallet. This will protect your BTC funds from rogue/untrusted software.