Advice on upgrading firmware on Ledger Nano I have the discontinued Ledger Nano hardware wallet.

Ledger have released new firmware for this for SegWit and to allow splitting BCH.

To perform the update, you have to wipe your keys and re-create them from your 24 word recovery backup. If for whatever reason this doesn't work, your Bitcoins are gone!

This seems a bit extreme/risky to me, because I haven't used my 24 word recovery backup before (what if I got 1 letter wrong in one of the words?).

Just wondering what way I should approach this? Would it be safer to transfer my coins to Coinbase temporarily, update the stick, and then transfer them back? I know I'd be hit for 2 sets of fees, but at least I'd feel a bit safer.
1st test your 24 word recovery backup with Electrum . Electrum as Ledger using BIP39 seeds. Crate new wallet with Electrum and choose " I already have a seed" then enter the 24 word recovery backup. 

You can do it from Tails live system if you worried of keyloggers. No need to  connect to internet if you don't need to see your balance but just want to test your seed.