1) Yes and yes- higher stat applicants do tend to get interviews first and it is also based on when you send in your application. The earlier you send it in, the likelier it is you will get an interview and be accepted. Also I think it's pretty well-accepted by the community at this point that IU gives a much higher preference to in-state candidates and interviews them earlier, so being IS will definitely be a huge advantage. My MCAT is much lower than IU's median and mean and they gave me an interview (I'm ORM too). I doubt that would've happened if I wasn't IS. High stats + early app= golden (provided your primary isn't trash). lower stats + early app or high stats + late app are more variable and I don't think anyone on here can concretely tell you what to expect there. Also, ORM/URM status plays a factor.
2) Not necessarily- it echoes what I said above. Having everything in order as early as possible will never hurt you and can in fact tremendously help you. Applying on the first day can definitely make you more competitive than it would have otherwise, as your app will *likely* (not definitely) be looked at sooner. The general rule is always the earlier, the better. Like I said, there are a whole bunch of things that influence when your app gets looked at but applying early is the only surefire thing we can do to increase our chances of being looked at earlier and more favorably. People saying their app was complete in Aug/Sept means different things for IU than at other schools. Being "complete" at almost any other school means that everything you mentioned (transcripts, AMCAS primary, secondary app, fees, LORs, etc) has been submitted to that school. You can typically monitor and verify this completion status on the schools' application portals when you're applying (you don't get a portal for IU unless you've been interviewed though, pretty sure they're the only school that does this). IU is also quite odd since they don't have a secondary. Being complete for IU pre-interview essentially just means your primary, MCAT scores, and LORs are in. The admissions office sends you a confirmation email to let you know this. If you receive an interview invite, then there's a plethora of other things you need to do before they give you a date.