Hi, Glennb, welcome to the forum.
Oh, one of my favorite topics, the Camino from Lisbon. I'm a big fan, because it goes through some very nice parts of Portugal. But the pilgrim infrastructure lags a bit behind until Porto. You will either have to sleep in the Bombeiros Voluntarios (firefighters) or in private accommodations, which run in the 20-25 euro range.
For starters, you should go to the Confraternity of St. James website and download the two online guides, one Lisbon-Porto, and the other Porto-Santiago.
http://www.csj.org.uk/guides-online.htm I just recently posted some updates on the Lisbon-Porto segment here:
el-camino-portugues/topic13007.html (but they are all pegged to the pages in the online guide).
I walked from Lisbon in spring 2009, and loved it. I never met another pilgrim till Porto, though. Since I walked, some albergues have opened and the waymarking has improved exponentially.
April could be a beautiful month, or it could be a rainy month. Temperatures will be pretty agreeable, I think, but who knows about the rain.
Buen camino to you, Laurie