Can this be substituted in any cake recipe on a 1:1 ratio? Like 1 cup of this GF mix = 1 cup of all-purpose flour?

Yes you can substitute one cup for one cup. However, having to eat gluten free for five years now, from experience I would recommend that you find a recipe for a gluten free cake. It turns out a lot better if you add Xanthum gum and extra moisture. GF cakes tend to be heavy and dry. That mix is similar to what I use and it does work well and tastes ok.

Gluten Free cakes also tend to cook faster than regular cakes, so watch the oven carefully!

I would love to know if you have found a GF recipe that you are able to use with tiered cakes? I have found that GF cakes, since they are heavier, don't stack well and cave in. Also any advice on anything GF would be appreciated as my daughter was diagnosed with Celiac 6 months ago and I am exploring everything!