Looks good to me mate. I think the limestone is a good addition but I'm not sure how it will go over time, it may turn to fine sand and slowly be watered out. I feel scoria is a good addition to any cacti mix but you certainly don't need it.
One other minor issue is the clay, firstly I don't think you need it (Ario roots are very good at extracting nutrients) and the gypsum will break the clay down where it will be watered out over a very short period.
That being said I have never used either ingredient I'm just basing this on my knowledge of each.
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