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Personally I always worry about the idea of slate in cages as it can split, fracture or chip & become very sharp so I wouldn't use it.
Not sure what those P@H stones are but if they're a slightly rough or porous rock they should be ok, resin can help a little but not a lot with keeping claws trim.
One of the best things is just a simple terracotta flower pot, if you lay it on it's side, fill it with substrate & hide food/treats in there they will dig around in it quite a lot.