I'd definitely take some care with the opening stretch. As you move along the Norte, you'll find that more and more of the albergues are open. But, between San Sebastian and Pobena in particular, it's easy to get caught by surprise.
The Convento is the albergue mentioned in that post, so you can't expect it to be open. I'd suggest walking from Deba to the Casa Rural Intxauspe (which has a pilgrim discount) and then walking the next day to Zenarruza where you can stay in the monastery. The Deba-Markina walk can be pretty demanding, but this will break it up more easily.
The Albergue Juvenil will be open in Bilbao, but I'd strongly advise against it. It's on the outskirts of town, not near anything of interest. Youth Hostel Akelarre is in a better location, on the other side of the river, and can set you up well for a superior, shorter alternative route to Portugalete. There's also a new youth hostel in the old town (Ganbara Hostel).
In Portugalete, I'd suggest Pension La Guia for a cheap, clean bed. Alternately, you could consider staying in Bilbao for two nights. On the second day, you could make the walk to Portugalete and then take the metro back into Bilbao. It's cheap, quick, and easy.
Not a ton of other options in Lezama, but Casa Rural Matsa is pilgrim friendly.
The Eroski Consumer site is worth a look (if you haven't already), just to get a sense of some of your other albergue options:
http://caminodesantiago.consumer.es/los ... del-norte/
