huge accomplishment - thanks for sharing the build journey with us. maybe you are not completely finished (-:
distortion? well see if adjusting the BFO setting improves things. this would be especially true if you can tune in CW nicely, but SSB is distorted.
most ubitx are not known for robust audio into a speaker - maybe a stronger audio amplifier is in your future. I tend to use headphones, so my v4 has enough audio. the RF chain does not have extra gain - so that a full sized antenna seems to be in play.
I am not yet using CEC firmware so I am not familiar with the S-meter. let's see who can help with that.
73 curt wb8yyy