Basic medieval fashion evolved from Iron Age fashion which came from Bronze Age fashion. I think Foundry's figures are based on clothing found from bog bodies dating back to the Bronze Age in Denmark.
Maybe the Irish wore the same, maybe they didn't.
Iron Age Ireland though probably had fashion similar to Britain which was similar to Europe and overall the fashion of the Celts, Germans and Dacians wasn't that different with trousers and a tunic and a cloak being worn by all. The differences would have been length and shape of cloak, brooch types, Dacians wore the Phyrgian cap which becomes fairly widespread in the later Roman Empire, the Anglo-Saxons wore them too. Other differences were hairstyles and facial hair.
The way I look at the middle ages is that in many ways, at least for western Europe, it was a return to how their ancestors lived in the Iron Age before the Romans. Power reverted back to local lords and their household troops, the church exerted huge control over politics.
The irony is that a late Roman infantryman with his trousers, flat oval shield, long sword was more like an iron age Celtic or Germanic warrior than anything the Republican or classical Romans would have recognised as a Roman soldier.Which is also why it's possible to use figures from different cultures and eras for variety as many have overlapping styles where the differences can be sidelined with a head or shield swap.
Bronze Age is not my forte but from what I've read horned helmets have been found from Scandinavia to Greece. So it's possible that Mycenaean figures could be used as well.
There is also organic weapons and armour that tends to get ignored. There was a bark shield found in Leicestershire dating back to the 4th century bc. Bone spearheads, probably javelins have been found all over Britain and even the Orkneys and also in Europe. These are Iron Age weapons too, not stone age, many were found in graves alongside iron spearheads.
I think as long as things look like they belong together and aren't obvious anachronisms like using a Roman in segmentata but painting the armour a bone colour, then do what you want, the Bronze Age is a real black hole in terms of information for places like Ireland.