Whilst miniatures for the Vinlanders is quite straight forward (indeed an order for some Artizan bondi was despatched yesterday), the Welsh are a bit more problematical. Despite a list of wars between England and Wales as long as your arm there appears to be a dearth of Welsh miniatures for the twelfth and thriteenth centuries or information on their appearance.
Gerard of Wales is the best source and describes the Welsh army of the period as a prince's teulu, or personal war band, supported by a large number of milwyr traed, or foot soldiers. These Welsh infantrymen, armed with little more than spears and bows, were lightly equipped so as not to impede their agility (indeed it is stated that they only wore one shoe so to help their grip in the mountainous terrain). Cavalry, whilst armoured, was not of a comparable standard to the Anglo-Norman cavalry of the period.
Looking through my bookshelf I've found one illustration of a Welsh or Cornish infantryman in the WRG Armies of the Middle Ages and one of a Welsh Chieftain in the Osprey Scottish and Welsh Wars 1250-1400. The basic infantryman is in a rough knee length, bare-legged with cloak and one shoe (!), whilst the chieftain has scale armour, cloak, round shield and looks very Dark Ages.
(photo Artizan Designs PAX003 Romano-British spearmen standing)
Miniatures wise I am going to try and hunt down some suitable looking Dark Ages Irish for the infantry, although I do like the Artizan Romano-British spearmen which might need a little bit of conversion but do look suitably Welsh. I'm not sure about command and cavalry, it'll probably be a case of going through the likes of Gripping Beast Dark Ages ranges and looking at Picts, Irish etc. to find suitable figures. Cavalry won't form a major part any warband bit a few pony mounted teulu would look nice.