For tank sides, in US construction styles, 10MM would be too thin. 12MM would be the correct size to provide an adequate safety factor. If it's using a eurobracing style, those typically can work with thinner material. I don't have any way to suggest on that since each eurobracing I've seen has been different from the other. In theory it works for thinner material, but I'd want to make sure the person doing the construction was experienced in that style.
For comps: 12.9MM = 3.8 safety factor, while 10MM is less than 2.5. Since eurobracing adds extra safety margins, they might be fine, but again, I'd require an experienced tank maker.
For bottoms, I don't really know what you mean by 'double base.' Do you mean laminated glass? Is it 5MM + 5MM laminated to 10MM? My guess is that 10MM is too thin (especially laminated) unless you plan to fully support the bottom. Since most people would do that anyway, I think that in that case, float glass at 10MM should be fine.
If you don't plan to use eurobracing, or are planning to use cheaper glass (expecially used glass), or don't have an experienced builder, I'd opt for 12MM.