From recent experience the 0915 from Porto can get busy - it was the only train in the valley with standing passengers when 3 cars only - but nothing else does (apart from commuter trains at the Porto end). You should be able to book tickets on the CP website, which tells me that Porto to Pocinho is EUR13.50, however there's no particular advantage. Trains are 2nd class only, ex-RENFE "Camel" DMUs. If you are lucky, the Miradouro set may be in normal traffic on one of the IR workings. OT: as you are staying in Pocinho, I recommend a visit to the Foz Coa prehistoric rock art site.