US101 is a major north south highway traveled by every sort of vehicle daily. Is it busy during the summer? Yup it is going to be busy. Especially the northern portion. Once you get south of Newport traffic thins considerably but can still be slow through any towns. Dont worry about what you might have read on the internet. But do plan on no more that 50 to 75 miles between stops and then park for a day or two to explore and see the sites. Without reservations it is going to be really tough finding camping along the coast this time of year in the state parks, but you might find some private parks to get into.