I think that one seeks an understanding of the essential ‘buddhavacana’ of early Buddhism based on early Buddhist texts does not become too complex now. This is because the following basic works presented in the English language useful for international communities by Choong Mun-keat provide clear direction and understanding for the studies in early Buddhism:
The Fundamental Teachings of Early Buddhism: A Comparative Study Based on the Sūtrāṅga portion of the Pāli Saṃyutta-Nikāya and the Chinese Saṃyuktāgama (Series: Beitrage zur Indologie Band 32; Harrassowitz Verlag, Wiesbaden, 2000).
“Ācāriya Buddhaghosa and Master Yinshun 印順 on the Three-aṅga Structure of Early Buddhist Texts ”, Research on the Saṃyukta-āgama (Dharma Drum Institute of Liberal Arts, Research Series 8; edited by Dhammadinnā), Taiwan: Dharma Drum Corporation, August 2020, pp. 883-932.