If you are going to be on and off buses and planes all day for your transfer KIX-NRT, why not take the train? Less hassle and more comfortable, and maybe get a decent lunch or some sightseeing out of it.

You can go KIX to Shin-Osaka or KIX to Kyoto, where you can take the shinkansen into Tokyo and then the NEX into NRT. Won't take much longer than your original plan by air.