Detritus IS the stuff these guys will eat; this is a standard detritus cleaning package...
I have a saddle valentini - inverts are not it's strong point. Altho I think the serpent could survive with my Toby, the star seems very fragile --- and cukes hardly survive, even for most experienced aquarists! (I have NO IDEA why in the world a cuke would be included in a standard detritus package.)
Perhaps getting the serpent separately (they arrive rather LARGE and impressive --- mine is in a reef, but I have considered putting it in the 45 with the toby). I wouldn't put a star in with the Toby; I've seen it go after an urchin that happened to get stuck upside down and vulnerable.
A suggestion for sand cleaning is the nassarius snail or the tongan super nassarius snail... These snails are real sandsifters, going in and out of the sand hungrily.
If you sandbase is deep enough, perhaps look to a sand sifting goby...?
BTW, I bought the same package... the star lost all it's legs within a week, the cuke was dead in a day or 2. Thank goodness for the 14 day guarantee!
Good luck.
Deb