Pretty sure I'm okay here
20A=2400w, 1300w bidet, ~160w fan, ~100w LED lights=~1500w which is less than 80%. Only possible hiccup is it is in a master bath with dual vanity so slight chance my partner and I will be sharing the room and they would be using a hair dryer at the same time I'm flushing.
To make life a bit easier I'd like to tap into the line in the attic prior to where the circuit first connects to the lights/outlets where there is already a junction box and run a new GFCI in parallel rather than extending from the last outlet in line in the bathroom already behind drywall that will likely require drilling through some studs.
This also leaves open the posibility to run a new dedicated circuit for this plug in the future if it ends up becoming a problem.
Anything I'm missing?