For an army of Gwynedd you wouldn’t have that many horsemen. In 1282 the Teulu of Llewellyn ap Gruffydd was around 160, though he did field up to 500 cavalry when supporting Simon de Monfort in 1256 (with allegedly some 30,000 infantry). Perhaps the remainder were scouts?
For comparison the army of Deheubarth had 600 infantry and 2000 cavalry at Crug Mawr in 1136.
But… depending on what rules you’re using you could justify having the whole lot mounted if you’re depicting a small raiding party off to reduce the cattle feed expenditure of the good people of Cheshire 🙂
Going from memory I think the south Welsh were the main archers and the North Welsh mainly spearmen, though they would have had some archers.
Shields? Depends quite what period you want. Traditional round shields would be appropriate plus whatever was picked up on service across the border.
Spears? I’d guess no actual standard length, but it would to some extent depend on the size of ash tree you had to hand… 🙂 That said the North Welsh are recorded as bracing themselves for cavalry using spears rammed into the ground in the early 13th century but other records say they threw spears. Given they are note as carrying more than one than could translate as a relatively long or heavy one for hand to hand and a javelin, But I don’t think we’re talking pikes here but a standard Dark Age length.
As ever the issue is with a scarcity of sources, inexact use of terminology and the fact that foreign sources may not be objective.