Seconding oxyclean or a similar surfactant for the cleanup.
Second piece of (possibly unwarranted) advice: Do your best to load the box in such a way as to minimize fiddling during active burn times. We have a small fire box so for us it’s usually a sort of Z pattern with two parallel logs and a cross piece. Play around with a few configurations to figure out the best layout for yours - the manufacturer may have suggestions. The goal is to set them up in such a way that the bottom logs collapse and let the top ones come down into the renewed coals, then turn to coals themselves. That’s the optimal time to insert fresh logs to minimize ash and smoke escaping into your residence.