The 4.5.5 OTA should effectively yield the 'factory reset' you were seeking. Note there is always a small risk with OTAs even those performed on unaltered devices. Amazon offers a one time non-hassle exchange should something happen (assuming it is still under warranty).I thought that the OTA would brick the device? I have no interest in rooting this thing anymore, I want to go back to standard Fire OS with nothing else (like the gapps). If I allow OTA, will it go to 4.5.5 and remove everything that was installed? I'm a little confused. Sorry to annoy you with so many questions.
Some OTAs can result in a bricked device; going from 4.5.2 to 4.5.5 should be safe.