Typically a 4" concrete slab is used for a foundation but with a 2-story ICF/concrete home, I was wondering if one needs to increase that foundation thickness due to the added weight?

For a mild climate area like Chino Valley Arizona, does one need to utilize EPS insulation underneath the slab? Or just pour the slab onto compacted AB?

Lbear; the slab typically does not bear the weight of the house, the footers do and codes require bigger footers for 2 - 3 story homes, your architect/ engineer should advise you on this

In a thickened edge slab, the edges are thickened for this reason.

I also read that doing "cut and fill" on slab-on-grades is not recommended for areas with seismic issues. Problem is that it is next to impossible to find a completely flat and level spot that requires no cutting and filling.