Well, he's never been to a wedding there so I'm afraid I can't help you. I used to use a castle in Northern Ireland who didn't advertise receptions as they didn't have the facilities to do put on the reception themselves BUT they did let you bring in caterers and have use of their tiny kitchen. They also let you put a marquee up in the grounds.
Check about their licensing laws as they very often only have a basic license which means you have to be cleared up and out by 11pm, and also the rules on smoking as your guests might have to leave the premisis completly to have a smoke as it's still classed as a public building even if it's hired for your exclusive use.
Good luck with all your planning, it's a very exciting time

Oh, OH says have a look at Carmarthen castle too. Apparently it's lovely and he knows they do a lot of weddings and filming there.