Hey Ed
You'll find the way- I did the Portuguese in June and September, and even in those few months everything has been very well re-marked. To pick it up in Valenca, the route runs on the Avenida de Espanha east of the fort, or failing that, your only option when you get to the International Bridge is to follow the way (right hand side of the bridge is the official way, but I prefer the left hand side as the signage for the border is more visible). There is a motorway being built south of Caldas so the route keeps changing, but although the details are frustrating, it is generally kept well-marked.
I haven't met anyone yet who managed to get a credencial in Valenca; everyone starting there has had to pick one up in Tui. On the plus side, the stamp at Tui is one of the prettiest.
Can't comment on lodging that time of year, but I'd agree with Whalleyranger; my big regrets are a)not having stayed in Caldas (where there is an albergue) and b)not treating myself to a balneario there. You'll have been walking, possibly in the rain, an added bonus of the balneario (my friends have followed recommendations to stay at the Acuna for 53euro for 2) are lots of thermal-fed of radiators to dry out your clothes!
I'm not sure of the protocol re: people linking to the Confraternity guides (Peregrina2000 has done south of Porto, you'd want the one by JohnnyWalker for north of Porto), so I'm not doing it here, but you probably will have found these already in your searching, non?