5 watts is well above what is allowed. FM used to be limited based on uV/Meter as measured from the Antenna. Not sure if It's still that way. AM was more forgiving, setting the limit to a specific amount of transmit power and antenna height above ground or the building your transmitting from, so there was more room the play with there.
https://www.fcc.gov/media/radio/low-power-radio-general-information