Multiple sound cards are things people get into later in their Retro adventures (if they take it that far) The really GOOD sound cards people talk about are rare and expensive, like the Gravis ultra-sound. So are the iconic sound cards, like the sound blaster pro 2.
I linked an ESS 688 sound card earlier that was partially plug and play, with a jumpered IDE port, which would likely work.
But yeah, fully non-pnp cards are going to carry a price premium, as they are rarer and more desirable, as you can see in this thread. You could give an ESS 1868 or Yamaha YMF-718/719 card a punt. I can't guarantee it will work, but there is a good chance, and they are pretty inexpensive. At the very least, I haven't had much issue getting these cards to at least work in DOS. Windows 3.1 can be more temperamental.
You can certainly try setting the hard drive as master, then the CD-ROM as slave, and run both drives off the one IDE cable, but because I've never tested this using your particular drives, I can't guarantee it will work either. Old computers can be finicky beasts.
Opposite to PNP is non-PNP, as in there really is no full opposite to PNP. Originally ISA cards were configured manually using electrical jumpers. Then software configured cards became a thing, particularly for network cards. Then PNP was invented as an out of band way to fully configure ISA cards and became the normal when ISA became old.
OPL3 is the music standard for FM synthesis before fully digital music and wavetable synthesis replaced it. I suggest the ess or yamaha isa cards because they are known to consistently implement OPL based FM synthesis well.