I'm supposed to copy and paste the private keys from the previously exported private keys file from Electrum. So I copy and paste some addresses, but the button to proceed (Next) remains grayed out, and I am unable to proceed.
This probably means the address (or private key) is incorrect. If it's correct, you can click Next.
However, even though I've never attempted this before, my understanding of the process was that I would create the wallet in Electron Cash by importing my seed (the 12 words) from the Electrum wallet, which contained my BTC before I sent it all to my Ledger Nano S.
You can: just create a new Standard wallet in Electron Cash, and click "I already have a seed". Unless you used 2FA on Electrum, in that case it becomes
slightly more difficult.
If you post any of your BCH addresses, I'll dust it for you to ensure you can't move your BSV/BCH-A Forkcoins. Just to be sure: you'll need to include my BCH-dust in the transaction you're going to send.