Background info, from Simon Inglis: The Football Grounds of Great Britain, 1987 ed
IRL in 1906 the FAW decided that the name "Cardiff City" would only be granted to the first professional side in the area, which happened in 1908. They moved to Ninian Park in 1910, the site (appropriately, many would say) being a 5 acre rubbish tip. before this it wa a stone pitch in Roath, and at Sophia Gardens public park.
Newport: at Somerton Park, an extant sports ground since formation in 1912. the club originated as a sportsclub of the Lysaght iron and steel works.
Swansea: the Vetch Field opened as a sports ground in 1891, with a cinder running track, and a turf track for horses. Cinder pitch and knee pads until 1913. Odd point: the pitch is east to west - as is St Helens rugby ground: a narrow coastal plain, and no room in the case of the latter, and existing buildings in the former case, made this necessary.
Wrexham: the Racecourse Ground was used full-time from 1905, the Ground ("a place where drunkardness and vice were encouraged to a terrible extent"*) had existed for decades.
* "Admirable extent", in my opinion.
So, grounds of some description in the 4 largest Welsh towns.
Getting from north to south Wales, and vice-versa, has never been easy - it's why they invented Birmingham - two regional leagues and play-offs ("Test Matches" in contemporary parlance) may be a better option.