this is where I need the most clarification. First, do you mean install a BCH wallet on my PC? Like Electron Cash? Second, what is mnemonic code? Third, you mean import it from Electrum (which should now have a balance of zero, having previously sent my BTC to my Nano)?
Correct.
After emptying your BTC wallet, use this wallet to send your BCH (by using your mnemonic code: the 12 or 24 words). Electron cash should be fine for that task.
Regarding the fees: They are relatively high currently if you want the transaction to confirm within a few blocks.
If you can wait however, you are free to create a transaction with a custom fee, to pay less overall.