Tobias’s questions:
“but the PS is akusala (defilements are not removed but added).”
There is a kusala-mula PS that removes defilements. That is the way to Nibbana:”Kusala-Mula Paticca Samuppada”
“Moha is a cetasika. Avijja is not moha, but a reduced form of moha. Is moha cetasika involved when someone does punna deeds?. Is moha cetasika involved when someone does punna deeds?”
Yes. Moha is a cetasika. Avijja is not moha, but a reduced form of moha.
When one does punna kamma, it is the avijja cetasika that is involved. However, if one has comprehended Tilakkhana FULLY (i.e., if one is an Arahant), it becomes a punna kiriya, without kammic consequences.
Difference between moha and avijja discussed at: “Lōbha, Dōsa, Mōha versus Rāga, Patigha, Avijjā“.