Prefix me- indicates the ACTIVE sentence when the structure is Subj + me-Verb + Obj. Ex. I eat an apple = saya memakan apel.
While prefix di- indicates PASSIVE sentence when the structure is Obj + di-Verb + Subj. Ex: The apple was eaten by me = apel dimakan saya.
Hope this helps
Your grammar theory is correct but I am so sorry that your example "Aku memulai buku" cannot be done (not work). We are not allowed to put buku after memulai directly as it will be ambiguous.
But, we may say, "Saya memulai membaca buku." Here membaca buku acts as an object for memulai.
Another example: "Siapa yang memulai pertengkaran ini?" means "Who started this fight?"