The second question might be easiest for the Brits on the board, but again, everone who knows it is welcome to share their knowledge Grin
2) The castles in Wales were built mainly by ...
a - the Welsh
b - the Vikings
c - the English
My money is on the English. Just finished watching "A History of Britain" which I cannot recommend highly enough and it covers English Edward I ("Longshanks") conquering of Wales, made the first son of the English King the Prince of Wales and built a lot of castle/forts to remind the Welsh of who was in charge.