First of all, your hobbies and passion projects absolutely are EC’s! Secondly, yes, first-gen does help - perhaps even more so now that racial preference isn’t an option for colleges in their attempts to build a diverse class.
Secondly, with a 1510 PSAT, you should at least be a National Hispanic Scholar and probably a National Merit Semifinalist, right? (I don’t think there’s any combination of subscores for a 1510 that fails to clear the IL cutoff, but correct me if I’m wrong.)
If that’s the case, you could go to an excellent and diverse CS school like UT-Dallas or UCF for free. What would your net cost be at UIUC?
Since you’re interested in California schools, consider Harvey Mudd and/or Pomona in the Claremont Consortium (depending on whether you like Mudd’s lab-science-heavy core curriculum or not… although if you don’t, you probably won’t like CalTech either). CS is top-tier, and the 5C’s could be a great environment for a creative student like you. (The Human-Centered Design curriculum in “The Hive” might be of interest Human-Centered Design - The Hive ) FWIW, Harvey Mudd is one of the very schools, short of women’s colleges, where the CS major achieves gender parity and even leans slightly female. Also, run the NPC for USC. Some NMF applicants get full-tuition merit, so it might work even if the need-based aid isn’t good enough.
Speaking of women’s colleges, consider Smith, which is very strong in STEM and also offers cross-registration with UMass Amherst, which has already been mentioned as a very strong flagship for CS. Also if Columbia is of interest, consider Barnard as well.
Hopefully Rice is included in your “other T20’s” list?
Additional strong CS schools that meet need but aren’t as reachy as the T20’s - U of Rochester, CWRU, Northeastern, Tufts, Lehigh, Lafayette, Carleton, St. Olaf, Grinnell, Hamilton, Vassar, Wesleyan. Run NPC’s for these to see how your net price may vary. I can especially imagine you enjoying the student-led design organization at Northeastern https://scout.camd.northeastern.edu/ It’s very software-heavy even though it’s based in the design school. (The CS+Design major there is also very cool, if that appeals.)
Hopefully someone more knowledgeable about this will chime in, but I believe U of Waterloo, which is a top-tier CS school in Canada, recruits students with AIME/USACO distinctions with merit money. I don’t know the likelihood of getting to your price point, but it might work, and it’s just as respected in CS as your aspirational US schools.
Good luck!