Are sound, smells, taste, and touch rupas? Are they also just a group of kalapas? What about light?
Sound, smells, tastes are all rupa. Hardness/softness, heat/cold etc are also rupa and experienced through the body sense.
Kalapas are composed of at least 8 rupa- the 4 mahabhuta rupa, color, nutrition and taste. Sound is an additional rupa that can arise additional with this minimal group.
The commentaries explain light as a supporting condition for seeing:
Vism XIV
39. And not only are the eye and visible data, etc., conditions for the eyeconsciousness
element, etc., [respectively], but also light, etc., are too. Hence the
former teachers said: “Eye-consciousness arises due to eye, visible datum, light,
and attention. [489] Ear-consciousness arises due to ear, sound, aperture, and
attention. Nose-consciousness arises due to nose, odour, air, and attention.
Tongue-consciousness arises due to tongue, flavour, water, and attention. Bodyconsciousness
arises due to body, tangible datum, earth, and attention. Mindconsciousness
arises due to life-continuum-mind,18 mental datum, and attention.”