I think you can afford for your list to be unbalanced, because IU as a safety sets such a high bar. As already mentioned, Hamilton Lugar is top-notch for IR; and there other fantastic options like the Policy Analysis major, which combines Poli Sci / Public Policy with a very strong base in quantitative analysis and data analytics - perfect for a strong math student, and a real asset when building a career in the field. (Plus, a top-notch music school with good opportunities for non-majors, including marching band if you want to continue with that… stellar for foreign languages… and all the education programs you would need.) I know that staying in-state probably doesn’t have the excitement factor of some of your reach schools, but an IU education wouldn’t be inferior to most of the other schools you’re considering, and a with a guaranteed full ride… not much reason to apply anywhere that you’re not 100% excited about.
What’s your goal with the education major? Is the conventional wisdom about going to school in the state where you want to teach applicable, or are you not thinking of going directly for teacher certification?
For another strong IR school that would be a low-match if not a safety, U of Denver and its Pioneer Leadership cohort program might be worth a look. They don’t guarantee full-need-met aid, but I’d think it very likely that you’d get enough merit to fill any gap. Lots of music opportunities there too (albeit no marching band - that was disbanded a few years ago when they got rid of football, although there’s still an active pep band), and education programs. I wouldn’t say it beats IU on any objective measure, but it could be worth a look if you’d like the location/vibe better.
Mostly, though, I think your best bet is to take a deeper dive in terms of the Questbridge schools, and figure out whether there are additional schools worth ranking (if clearly preferable to IU) or at least keeping on a “maybe apply RD through QB if not matched” list. Macalester, for example has a strong reputation for Poli Sci, International Studies & International Development. If you’d consider the west coast, the Claremont Colleges could be worth considering (Pomona, Scripps, and Claremont McKenna are all QB Partner Schools), in addition to Stanford (huge reach but no harm in ranking it!). I know you said east coast because that’s where you see yourself (and I’ll infer from your list that this really means NORTHeast); but going through the whole list of partner schools and making sure none of them gives you a reason to widen your geographic preferences would be worth a a bit of your time. I agree with Tufts as a possible addition - potentially BU also - and I think Wesleyan, already on your list, could be a great choice (in particular, the CSS program/major).
I think you’re going to end up with great options; and if UPenn ends up being your top choice, I think your odds at QB/ED are not bad (although of course there are no slam dunks at this level of competitiveness, short of athletic recruitment). Good luck!!