Welcome to Mosaic! I hope you enjoy the program.
I honestly don't even think the GAs look at whether someone is Mosaic when assigning seats. I've posted about this before but I had an experience a couple years ago as a Mosaic where I was reassigned FROM my EMS seat that I paid cash for to something in the back with no explanation whatsoever. Also no refund. I was fortunate that the station manager was on my flight and at the gate area and very quickly put me back into an EMS seat though it wasn't the row I wanted. I hate Row 1 on the E190 and that's where I ended up. I was also compensated immediately and generously. But I had to go through a whole issue that shouldn't have happened to me in the first place.