Yep Cardiff is easy launching with lock gates which are pretty much 24/7
Don't know the Welsh Coast so well...but The Devon side is lovely...and from Porlock down very Scenic!..you can get in a few places but ONLY over High Water,so timing is imperative if your thinking of going ashore.
Minehead....Lynmouth...Clovelly..and Ilfracombe...where at a push you can get fuel,but involves a walk!..Should be plenty of Wildlife about here on in,and the fishing can be really good!
Of course the real Jewel is Lundy....easy to do in a day with decent weather and about 60nm from Cardiff...just moorings there,but a large Jetty for dropping off...No Fuel.
As an aside I'd say make sure you're anchor ect is readily available and up to spec!....with the exceptional Tides it's not the place to be drifting about in the event of any problems.
Great wild Cruising and like nowhere else!