http://www.csj.org.uk/route-coastal-route.htm
That above link may help a little. If you start in Irun it is 825km to SDC. That would mean you would have to walk a massive (impossible?) 59km per day.
If you know roughtly how many km you can walk each day you can then calculate backwards from SDC and start there.
The other option is to walk as much as you can without pushing yourselves and then get transport to Madrid.
The Camino will still be there for you to come back in future years and pick up where you left off. Many people do the Camino in stages over two years upwards.
Finally you could walk to one of the big cities and then take transport to a point further down the Norte, so "jumping" a section(s).
Remember that to get your compostella you MUST walk the last 100km which means making sure you have the sello from Baamonde (or other) and then as many sellos as possible. The Cathedral will accept the odd sello from a bar, but will expect to see albergue, town hall and church sellos as well. In 2010 I saw a lady with a credential full of bar sellos refused the compostella.
As to the albergues you would (a) need a guide book and (b) the advice of those who have walked the Norte.
I have only walked the last 112km (just before Baamonde) so I cannot be of much use except to say that the municapl albergues accept no reservations. It is first come, first served, but if you turn up in a taxi they will probably turn you away. The Norte is much less popular so I doubt that you would struggle to get a bunk. Once you get to Arzua, where the Norte joins the Francés, then it might be more difficult though private albergues are also available. Monte de Gozo is huge, so less problem there.
I think your friend is right to be worrying, but you can resolve this before you go and still have a good Camino.