Yes, Siebe. Your above descriptions are mostly correct. Specifically:
“I have understood, but correct me if i am wrong, that the javana citta’s of an arahant are not akusala anymore but also not kusala.”
Correct. Arahant’s citta can never be akusala; they are not kusala either (because there are no “ku” or defilements to get rid of “sala”). But they can be punna kamma. See, “Kusala and Akusala Kamma, Punna and Pāpa Kamma“. They are called “kriya citta”, which just lead to actions.
“Behaviour based on gati is Always reactivity and cannot be called noble.”
Yes. An Arahant has removed all gati (for the same reasons that he/she does not generate any kusala/akusala citta mentioned above).
But an Arahant may still have some kammically neutral habitual actions. A young Arahant jumping over mud puddles mentioned in the Tipitaka is one good example. Another Arahant actually could not help uttering “rough speech” out of samsaric habits. But there was no javana power in that speech. This is why we cannot judge other people; they only know that they did not have bad intentions (no dosa cetasika in those cittas).