47lincsled - the answer is "sometimes yes and yes.". The Bamboo X1 printer does such a great job that often the parts are so smooth they don't have visible lines after printing or once primer coated are no longer visible. But in the case of curved parts, those will usually have some kind of grain or lines somewhere - then I do both, lightly sand and/or use a putty then sand to remove the lines, esp the cab and wheels. Bonded joints typically I fill with a putty and sand them smooth. before painting. The lower hull is 3 printed pieces bonded together. The join lines are filled and sanded for example.
Thank you glad you enjoyed the project so far.
Bob