Congrats on the purchase. I have a 2018 so the mods might be bit different than your 2019. With that in mind, here's my "must do" if I were starting over again:
Performance:
1. SVC Intercooler - stock one is small, too small imo, for the power these turbos can generate.
2. Gearhead tune. Uses the octane sensor, doesn't appear to mess with the warranty. (Of course, I hope to never test this theory).
3. 1 degree less spark plugs (2018's use the Motorcraft FRL0043V)
4. Replace the stock resonator and exhaust to personal preference. Stock exhaust was corked up imo, and once I Borla'd up, motor rev'd quicker and sounded better, but I did lose some bottom end until the tune was installed (which is why I listed the tune above versus the way I did it).
Suspension:
1. Leafs, coils, bump stop kit (I'd suggest Icon, Geiser Bros, and SVC with Fox bumps). I went with Deavers, probably going to switch to the Icon leafs and doing the coil springs is a good mod until you figure out which direction you're going with the suspension.
Interior:
1. Forscan - Read up on it, learn how to use it, it'll change your life (or at least give you the ability to change many things on the truck). Great way to disable the fake exhaust sound, autostop, and various warning chimes. Also, one of my favorite mods was simply changing the indicators to flash 5 times versus the stock 3 when you tap the turn signal lever, great for lane changes.
Exterior:
1. Tint all the glass, including windshield.
2. Stubby antenna. Many have mentioned it and I too highly recommend it as the stock one can get a bit whip-like.
Bed:
1. Tonneau cover. I went with the Retrax pro, no complaints.
2. Builtright bed rack system. Easy to install and very functional.
Cheers.