However, if my plan is to delete Daedalus after creating the wallet, the spending password becomes obsolete, correct?
correct, when u will restore the wallet u can choose same or different spending password
What if Daedalus is no longer in use when I decide to restore the wallet or if I just decide to use a hardware wallet 5 years from now? Is the mnemonic universal for all future software wallets or do I need a
this was created using Deadalusnote alongside my 24 words?
daedalus will be available many years from now, it’s the official (IOHK) wallet for cardano and it’s running like a node (will download a copy of blockchain locally); also you can import the daedalus wallet in Yoroi (Emurgo wallet) and also on adalite.io, for sure in the future will be another options (be carefull that the daedalus is available only for desktop, there is a fake app for mobile - DO NOT USE IT!!!)
Also u can store the funds on LEDGER but ledger has own 24 seedwords which are not compatible with ADA wallets for the moment, so you will can’t restore the ledger in daedalus, yoroi or adalite.io
THE IDEA IS TO BKP THE 24 SEED WORDS as better you can (offline), but more copies (on paper, on usb, etc )