These days around 50-60% of new hire pilots at major airlines come from a civilian background. The military pipeline is smaller than it used to be and with the hiring numbers we're seeing, they can't source as big a percentage from there anyway. The civilian path is very viable.

You'll need a degree, but it doesn't really matter what its in. I suggest you do not "double down" with an "aviation degree" and instead get something you can potentially use as a plan B if you later choose differently or can't fly for whatever reason. GPA is important, so get the best grades you can, but if possible try and get a good degree you can use to make good income versus a "basket weaving" degree.

You can fly during college, especially if there is a flying program there, as well as concurrently at separate flight schools. Or you can knock out your degree and then learn to fly right after. Stay flexibile, keep your driving record as clean as possible and obvoiusly stay out of trouble. When you do start flight training, try and keep it as condensed and congruent as possible. Save your money and time to knock out at least large blocks/ratings at a time, rather than scrapping to log 1 hour every few weeks as you'll just end up spending more repeating lessons just knocking the rust off.

Find a way to build time after your ratings. Instructing is not the only way but it is one of the better ones for a variety of reasons. There will be a need for instructors too. Focus on that, and avoid mirrage opportuities like some "corporate" gigs. For low time pilots it may seem like a quantum leap to go from instructing/check hauling/banner towing/etc to get to fly anything turbine, but there are a lot of "jobs" out there that are absolute quick sand. Particularly be aware of part 91 single pilot planes where you will sit right seat and "double log" PIC with the other pilot. Every airline hiring department knows this trick. More importantly though, many of those jobs require you to be completely available 24/7, yet you won't end up flying that much.

Its way better to smash bugs in a C-172 for 75-85 hours a month than to get 10-20 hours a month of questionable King Air or Citation time. Once you get your 1500 hours then you can consider things like that, but make sure its legit from a logging perspective.

Keep your logbook updated and get really good at filling out extensive airline applications. Make a history now of everything since you graduated high school. Every address, every job, every speeding ticket, every period of unemployment for any and every reason lasting more than a day or two.

Avoid debt as much as possible. Even when you start making decent money (however you define that) don't spend to the limits of your credit and live paycheck to paycheck, because the industry really has a way of punishing people who do that.

Good luck, you are getting in at a pretty good time historically.