He already holds the Open Era record at nine. He would tie his record for most wins at a single tournament, which he just won his tenth Monte Carlo Masters.
I doubt Wawrinka wins, but I think he's probably the only guy on tour that could push Nadal on clay at the moment. So it's the best possible match up.
I wouldn't say Thiem's win in Rome was a fluke. It's just a different animal when you're deep in the second week of a Slam, against the greatest clay courter ever, who's playing supremely confident, and Thiem was probably already satisfied with himself for his performance against Djokovic. Bad combination of things. It's good for Thiem that he was able to knock out someone like Djokovic in a Slam. Someone like Dimitrov has been in multiple Slam matches with Murray, Djokovic, and Nadal that he was controlling and should have won... but he didn't. He's got that one Wimbledon win over Murray a few years back, and he hasn't done anything since. So it's up to Thiem to keep improving and building his game.