re: counting words after pi
a b is always right-- not controversial
a pi b, in my mind, means a has a universal relation with b. But a b means that too! Juxtaposition (words next to each other) and pi constructions are closely related. This is fairly uncontroversially wrong.
starts a new phrase modifying the previous with a noun at the heads and modifiers afterwards
a b pi c d, is alway right. not controversial.
a pi c d as a whole modifies another word or phrase.
a pi b pi c d = (a (b (c d)), and imho is valid. The middle pi phrases however are followed only by one word. The tail must still be two words.
Now moving into the land of "jan nasa li wile ante e toki pona"
pi overlays. Sometimes a phrase that represents 1 thing in the real world has a prepositional modifier, e.g. , telo suli lon insa ma. When used as an object, it looks good. When used as a subject, it get complicated:
jan lawa li weka e telo suli lon insa ma. The government drained the swamp.
*/? telo suli lon insa ma li tawa tawa. The lake rippled. Prep phrases are not allowed before the "li".
telo suli li tawa tawa lon insa ma. This is okay, but it splits the the phrase. Splitting phrases makes sentences harder to read.
telo suli pi insa ma li tawa tawa. This is a pi overlay. This is syntactically correct, not controversial. But some information is lost. pi is less specific than lon.
telo suli pi lon insa ma li tawa tawa. This idea is from jan Kipo, which has some merits, but so far no one has started using it.
*/? telo suli pi ma li kama ala. The aquifer dried up. Many set phrases containing prepositions have only one word after the preposition and when the preposition is dropped, the sense is change too much. telo suli ma li kama ala, in my opinion isn't really the same thing, it would be closer to "the mud dried up" The effect is more pronounced when the phrase is something well established.
telo suli pi ma ijo li kama ala. Grammatical, but now we have a place holder modifier. This makes the language harder to learn.
li pi as a verb
Official, but not in widespread use, violates something deep rule about mixing content and function words or because this just lacks any parallelism to the other valid constructions. This construction wouldn't necessarily have 2 words after pi.
moku li pi mi. I have food.
In my opinion, mi jo e moku is preferable, or moku li lon poka mi, if you prefer to calque languages that use spatial nearness to indicate possession.