I think like everything else with electrum, it's pretty self explanetory and the software gives you a lot of information.
It is quite strange that ledger would point you to that, as I see it, electrum probably works better.
I found this topic which looks quite informative, it is from a few months ago so not sure how useful it is: https://bitcointalksearch.org/topic/anyone-use-a-hardwarw-wallet-with-electrum-1860569
As a side note, it may currently be impossible to put it on electrum if you're using segwit addresses instead of legacy addresses.
If you coins are in a legacy address you should find that it should work well.
Once electrum is downloaded from electrum.org/#download all you need to do is run it, select "Use a Hardware Device" and it shoud search for your wallet. It shouldn't even need any authorisation from the ledger when you start it as all it needs is the unencrypted data - mainly the public key.
If you do this it's useful to keep your chrome add-on just in case but eectrum proably has a lot more features (or is at least easier to handle as its open source and has at least 4 main developers - I think).
Thanks. Given that I have an existing Electrum wallet that exists outside any knowledge of nano, do I surmise that I create a new wallet in electrum, and point _that_ at the ledger?
I need to think through whether I want my cold storage -- even if unable to transact without the nano -- visible on a day-to-day computer.
HCP's guide above is quite a good one → follow that!
I think there was a hidden question in your post, electrum can handle up to 5 wallets for instant access. Just click file>"wallets" and you can navigate between them.
You can have an unlimited number of wallets (though I really wouldn't suggest this as once it gets over five, you'd have to go to file>"new/restore" and enter the name of the wallet you want to go to).