I think the key is to let the dough rest longer before rolling it out. If you work it too soon the gluten tightens up and you get a tough crust. I usually aim for at least thirty minutes covered with a damp cloth. Also try using ice water instead of tap temp. That makes a real difference in keeping the fat solid which gives you those flaky layers. For the filling I would suggest cooking down the apples first with a little lemon juice and cinnamon until they soften but still hold some shape. That way you avoid the soggy bottom problem. Let me know how yours turns out. I can send you the measurements I use for the butter ratio if you want. I have been tweaking that part for a while now and finally got it where I want it. The trick is to not overwork the dough once you add the liquid. Just bring it together until it barely holds and then let rest.

I think starting with a medium-high heat and then lowering it once the surface is seared works best for thicker cuts. For the seasoning I would keep it simple with just coarse salt and cracked pepper applied about forty minutes before cooking. That gives the salt time to draw out some moisture then reabsorb which seasons all the way through. As for timing it really depends on thickness but a good instant read thermometer takes the guesswork out. I usually pull mine off about five degrees before target temp and let it rest under tented foil for at least eight minutes. That rest period is crucial because it lets the juices redistribute. If you slice too soon they end up on the cutting board instead of in the meat. Let me know what thickness you are working with and I can give you a more precise timing.