Elaine --- Something to consider with limited time are your rest days. I assume you'll take a day or two extra in Santiago to rest, sightsee, visit Cathedral, etc.
Eight or nine days from Barcelos to SdC may be long enough that you need a rest day prior to SdC if your body isn't well conditioned. If you're a strong, long walker, then no worries about a rest day.
If you start from Valenca, then you have five or six days to SdC, and you can use your time in SdC to rest and play before you go out to the coast.
I'm hesitant to recommend anything that lands in the personal preference category because I don't know you, and what I like may not be what you like. However, I personally love staying in a private hotel on the beach just shy of Finisterre, but I come from a landlocked region, so the ocean is a major attraction for me. Thus, if I were in your shoes, I would start in Valenca because I would want to spend time on the beach eating percebes and drinking brandy. But that's just me.