My experience comes mostly from re-wiring a G&L bass. I have mine wired so that I can select series, parallel, single-coil-bridge and single-coil-neck. Series and parallel are good settings, although I don't use the parallel much. It's similar to the single coil but loses a little of the sparkle. The difference between the two single-coils is so subtle that I can't really tell them apart. If it were me, I'd just do one of them. You could do that with a three way rotary.
Alternatively you could add a tone cap to the fourth position on your switch. Lots of ways to do this, but since you are setting up for SC modes... On older G&L basses there is a .1u cap between the coils in the series setting. This gives the pickup a boomy sound and is referred to by folks who have them as the OMG cap. I have a switch on mine to take the cap in and out, which you might wire to the 4th position on the rotary. This would give you two series positions. If you like a boomy sound it's cool to have, but I mostly run without it. It's a tad too boomy, and unbalances the coils so it's not quite humbucking with the cap in. That said, it would give you four really distinct sounds.
I don't see much reason for two tones or two volumes on a single pickup bass...unless you want to do something like the PTB wiring...also something on G&Ls...
You might take a look at the wiring diagrams done by Ken Baker at "Basses by Leo"
https://www.bassesbyleo.com/
https://www.bassesbyleo.com/passive_l_series.html