You are asking about the conditions on almost 2000 miles of roadway. I can assure you that almost every condition imaginable exists somewhere along the way. It is impossible to generalize. I wish I could tell you that 27.3% of the distance is on a wide shoulder and 7.2% is on a separated bikeway, but I don't think anyone has compiled those numbers.
Having said that, I'll try to give you a perception. These are the most common conditions:
- A fair amount is on the shoulder of US101, especially in Oregon. In most cases, there is a wide shoulder, good pavement and moderate traffic. You will feel safe, but there will be traffic.
- Some of it is on small county roads, especially in Washington. There's no shoulder, and the road surface is mixed--sometimes quite good and sometimes otherwise. I remember a few roads that are quite rough, but only for a few miles. Trinidad Scenic Drive in Northern California springs to mind. Traffic will generally be very light.
- Some of it, as little as possible, is on moderately busy highways with a token shoulder. You won't like it, but such conditions are impossible to completely avoid. Such conditions are more common in Southern California. I remember the 27 miles through Malibu as being particularly bad (since Malibu has no beach path).
- Some of it through towns is on city streets, with or without bike lanes. You pretty much know what to expect there. Small town streets are no big deal, but you will be on city streets in LA for a few miles.
- There are a few separated bike paths. Not many. In Southern California, many of the towns have a beach path. Most of the route through LA uses those. There's no worries about cars, but you have to watch out for kids and dogs and surfers and skateboarders and picnickers and what not. There's a great separated bikeway south of Carpinteria that you will use.
I would say that the Pacific Coast Route is a bit more dangerous to cyclists than some other routes such as the TransAm and Northern Tier, primarily because those other routes use a lot of the tiniest roads you can imagine. The scenery makes up for it. For example, Big Sur (if the road was open) isn't particularly safe cycling but it has some of the most gorgeous scenery in the world.
I'm not sure exactly what you mean by "1,8 cm / 0,7 inch tyres". 1.8 cm is way too wide, and 0.7 inches is way to narrow. Nevertheless, you will be fine with regular road tires in most places, and you'll get by with them everywhere else. If your road bike will fit 25mm or 28mm tires, I'd recommend you use them. The heavier your load, the more you will appreciate wider tires. Skinny tires under heavy loads put a lot of stress on the spokes, so have a good wheelbuilder make sure your wheels are as bulletproof as possible.
