In Riddle's shoes, I'd prioritize. He tries to do too much at once, and, partly as a result of that (as well as, as I mentioned, the quality of the people he attracts to his cause) he ends up back where he started from. Were it me, I'd either focus on taking over magical society, here in the UK and abroad, and then worry about immortality, or else achieve immortality, whether by reverse-engineering the Philosopher's Stone or in another way, and then go for Supreme Power. Ah, well...his foolishness will make him much easier to deal with, directly or through my stooges, when the Day comes. Right now, he serves a purpose, rather like a Muggle stage-magician's purposeful misdirection of his audience. With everybody focussed on "Lord Voldemort, He-Who-Must-Not-Be-Named, the Most Evil Wizard In The World" nobody pays attention to me, even when I'm leaving clues everywhere.