These notes are from our experience on the northern route. I do not know about the others other than to say that the French route is by far the most popular. You will share the route with a lot of people and possibly need to be more creative about finding a place to stay.
We just showed up and started walking. We flew into Bilbao, but if I did it again, I would just fly to Madrid (cheaper) and take an ALSA bus to Irun, or San Sebastian. ALSA has very comfortable and clean buses that run on time. We used ALSA to to go Irun from Bilbao and to return to Bilbao from Santiago. In Irun, and in all cities, check with the Tourism Office (Oficina de Turismo) and ask for the Albergue de Peregrinos (Pilgrim's Dormitory). Those are the least expensive, usually 5 euros and normally have kitchens, and sometimes have washing machines (clothes driers are a luxury). Note: Many albergues are in schools and do not open until July, when schools are out for the summer. We started on June 20th and had some problems finding albergues until July. We did not stay in Irun, but did go to the albergue to get our "credencial", which is used to verify your stay at albergues so that at the end of the journey you get your "Compostelana", a very nice certificate that indicates that you completed the pilgrimage. We spent our first night in Hondarribia (5kms from Irun), in a hotel (San Nikolas). After about 24 hours of travel we did not want to stay in a dorm.
There are several types of albergues. The "Albergues de Peregrinos" are the official albergues, usually run by the local municipality. There are private, for profit, albergues that are sometimes worth the 10 euros or so. There are "Albergues Juveniles" (youth albergues) that I found to be disappointing (expensive and not so good). I preferred the official albergue, followed by the private ones. The best albergue is in Guemes. I also highly recommend Via Lactea (private in Arzua), the private one in Buelna and Luarca as well as most of the official ones, I particularly liked Baamonde and La Isla.
OK, so you have your "credencial" and spent the night in Irun. Get up early (we usually started at 7 am). Have breakfast in the albergue and follow the yellow arrows, shell markings or other indicators to the next albergue. As you walk, at the first sight of an open cafe, you might want to give yourself the luxury to have a "cafe con leche", basically a cafe latte for 1 euro or so. Use all the sugar they give you. Don't worry, you'll burn it off. The yellow arrows marking the route are ubiquitous on the route so there is little chance of getting lost. I also had a map that I used just in case. Once you get to the albergue, you pay and get your stamp. We normally showered, took a nap, bought food for dinner and had most of the afternoon and evening to sightsee or go to the beach (it gets dark after 10 pm).
One place that is worth spending two nights is Donostia (San Sebastian). This is one of my favorite cities in the world and has an amazing beach. We stayed at Ulia (right before) and La Sirena (at the end of the city). It was a gorgeous day to spend at the beach. Unfortunately, I do no recommend the La Sirena albergue (second night). It is a expensive for what you get. On the other hand, its cheaper than a 200 euro hotel. If you start in July, you will be able to stay at the official albergue.
Your feet are your primary assets. Take care of them. We had good wool hiking socks and polyester liners. The liners keep your feet dry and also slide against the socks to that the socks don't slide on your skin and crate blisters. Europeans favor light, high thread count wool socks without liners. If you do get a hot spot, buy Compeet at the ubiquitous pharmacies (you will see them easily by thigh neon green crosses that mark them). We ended the trip without a blister!
As far as guides go, I used this one, but it's in Spanish.
http://caminodesantiago.consumer.es/los-caminos-de-santiago/del-norte/Here is more information in English
http://www.csj.org.uk/route-coastal-route.htm
By the way, we plan to do the Camino Primitivo in a couple of years, followed by the Portugues in a couple more and the popular French in the Xacobe year of 2021.