This has always been a very interesting topic to me. I have a theory that another branch of his plan has something to do with the makuta scattered across the Matoran Universe. I think he deployed some of his most powerful makuta to eventually take over each region and then Teridax would become a ruler of an entire universe. (entire meaning that he didn't know about Spherus Magna and all the stuff around that.) He would probably find it easier to put Mata Nui to sleep, obtain the Mask of Life, kill him, bring him back to life, and take control of the Mata Nui Robot. He would then become the "Universe". He could want every intelligent being in line through his troops so he could romp through the universe doing what he pleases. I would also like to point out that, as much as he hates the Barraki, they were his inspiration for taking over the universe.