I've done one (extra) long distance hike - the Idaho Centennial Trail. It's about 900 miles, which is much less than what you're talking about.
I will say that you better develop some badass calluses before you go. Even though I hiked a ton before my trip, blisters were a big issue. Also, towards the end my achilles tendon started to hurt, and still hurts occasionally to this day.
Also, break in your boots before you go. Bring an extra pair of tennis shoes or sandals (I actually forgot to do this and was stuck with only my Red Wing boots for 10 days in the beginning).
I would also work out quite a bit before you go. Strengthen your legs, core, and back.
What you're doing is quite an adventure, though. Definitely not something to take lightly.