Welcome to the circuit.
What can I do to raise my chances ? Keep your GPA up. Since you can still control this, keep it as high as possible and don't let it be a setback for you when applying to units.
When should I get the AFOQT ? When/How do I start preparing ? You can take this whenever you'd like. I would suggest a good block of time for studying. I studied for a month straight to get the scores I wanted. You can take the test twice, keep that in mind when scheduling it, probably during a leaner time during the semester. Buy books such as Barron or Trivium. Make sure you find out your weaknesses and focus on those. Then take practice test after practice test. Timing is one of the most important factors.
Is there an internship program for students where I can get in touch with a squadron ? I think I heard of something similar from friends but I couldn't find any information. Never heard about an internship. Guard/Reserve is becoming so competitive these days that many squadrons don't really allow that type of "unfair" advantage to applicants anymore. Best bet is to target squadrons you want to fly with, save your money and rush them.
I have enough money to fly gliders but not for a PPL. Should I start now and rack up more flying hours in gliders, or just save a bit more and get my license ? I would not waste money on gliders and just aim for the PPL. It's already expensive as it is. Unless somehow glider hours can translate to some hours in a PPL, if not then don't bother and just focus on the PPL.
Should I major in something easier or continue with what I like ? Science is my passion and I'm not steering away from any challenges, but if getting into an easier major will get me closer to my dream then so be it. Nothing in life is guaranteed. You can get picked up by your #1 squadron right when you graduate and then fail your FC1. What then if you majored in something easy? Major in something you can see yourself working professionally in. Excel in that major and do your best. It will help you out either way. Plus it could look like a cop out when squadrons are reviewing your transcript and they see you switched from BioChem to Basket Weaving.
When should I start rushing squadrons ? and more importantly, how do I get started ? There are no fighter squadrons in my vicinity so there will be some traveling to do. There is only a C-130 base in my state but they are very clear on their website saying they don't want any visitors unless hiring (not sure because of corona or just in general). There is also a B-2 squadron in the neighboring state, but one could only dream to get hired by them. You can rush squadrons whenever you like. Though, I believe most require you to be within 90 credit hours of graduation, or a semester. So by all means if you have the resources start rushing and building rapport with the squadrons you want to fly with. If resources are a limiting factor then I would just wait until eligible and then go all out.
Last but not least, is it too ambitious to hope for a pilot slot straight out of college ? Not at all. I know many who are in the last semester of college who got hired. It's all about how you fit into a unit and how competitive your application is.
Don't be too discouraged with all the COVID stuff going on. It will pass and the way squadrons hire will also go back to normal. Good luck!