You're doing the right thing!
We stopped for a couple of nights on the way to the
Med and left there two seasons later. In those two seasons we used Marinas 4 nights and that was for social reasons rather than stuff pertaining to the yacht. Arousa is probably the easiest to explore and get a feel for the place with good anchorages within short sheltered distances just about everywhere. The north
wind can be a pain but there are plenty of windward shores to
anchor under and no real katabatic problems.
The worst problem we came across was the Spanish habit of disco
music till 5 am, so if you get a hint that a village is doing a fiesta, move. The all day long fireworks are a bit of a giveaway.
If you need a helpful boatyard run by an ex-liveaboard, <info@xufre.es> is the place to look. Nito is really helpful and knows most of what you could want to know and in good
English.
If you wish, I can send you a .gpx track which will show you where we anchored although it is rather incomplete. Cambados was the only place where
depth was a problem and there a couple of fisherman came over to specifically warn us about rocks in the vicinity. I can't imagine that happening in
England. They are really nice people and the whole set of Rias up to and including La Coruna are great.
Just do it.