Porto's metro line B stops at Santa Clara (on the outskirts of Vila do Conde), which is right on the connecting route between the Coastal and Central paths. The distances work out the same: according to the
Brierley guide, if you started at Vilarinho, it would be 8.5km to Arcos, whereas if you started at the Santa Clara metro stop, it would be around 8.8km to Arcos. Both routes to Arcos are on roads (except for 1-2km slightly more scenic woodland on the Central, also accessible if you take a little detour on the connecting route). Anyway it's something to consider, as the metro is regular and runs all day from 6am, so might be more convenient.
[p.s. TulaB the metro allows bikes, so long as they are placed in the rear carriage:
https://en.metrodoporto.pt/pages/402]