1. Khandhas are all mental.
In other words, the khandhas of rupa, vedana, sanna, sankhara, and vinnana are all mental.
2. Rupakkhandha refers to information of rupa.
My current understanding of the distinctions is as follows:
Bahidda rupa (distorted, altered rupa), ajjhatta rupa (XX vinneyya rupa)
3. Vedanakkhandha refers to the processing of sensory input
It is connected to tanha.
I currently understand the distinctions as follows:
Sukha vedana, dukha vedana, adukhamasukha vedana
Bahidda vedana, ajjhatta vedana
4. Sannakkhandha refers to the contextualization of sensory input
It is connected to avijja.
I currently understand the distinctions as follows:
Bahidda sanna, ajjhatta sanna
Kama sanna, rupa sanna, arupa sanna
5. Sankharakkhandha refers to how one reacts to rupa.
It especially addresses whether or not kammic energy is generated.
My current understanding of the distinctions is as follows:
Bahidda sankhara (kiriya), ajjhatta sankhara (abhisankhara)
6. Vinnanakkhandha synthesizes the above three (nama).
My current understanding of the distinctions is as follows:
Bahidda vinnana (vipaka vinnana), ajjhatta vinnana (kamma vinnana)
7. Through the khandhas, the following can be understood:
Rupakkhandha and vinnanakkhandha help distinguish between nama and rupa.
Vedanakkhandha helps identify the cause of tanha (craving) (samphassa ja vedana).
Sannakkhandha helps resolve avijja (ignorance) (by cultivating anicca, dukkha, anatta sanna).
Sankharakkhandha helps understand the formation of karmic energy (abhisankhara).
Please let me know if there are any errors in my understanding.