I forgot, the layer lines are not a problem if you wet sand PETG with 220 and than 400 grid. The primer will just help with a few areas that still remain imperfect. I prefer to build up the foundation with thin layers of primer as 3D prints may have some details that are not as crisp as they could be (corners). I will sand with 1000 grid before final paint. I could always print slower for better detail, but this already takes almost a week to print. On this model I also don't want to obscure the gradation or labeling too much. Many print with PLA as it is easy and fast to print, but I find it too hard, brittle and annoying to work with. ABS is nicer to work with, but the shrinkage corrupts dimensional accuracy required here and often leads to layer breaks in more solid models even if you print in a heated enclosure.