I always thicken with corn starch too. A book I found helpful is Marjorie Hurt Jones' The Allergy Self Help Cookbook. Early on in it she lists a whole variety of flour options with notes as to which ones work well for thickening, coating or baking.
For baking cakes, cookies, etc. I go either with Bob's Red Mill GF all purpose flour, or I use some of the suggested recipes that combine brown rice flour, white rice flour, tapioca starch and maybe a bit of sweet rice flour (or maybe also include sorghum flour or garfava flour. The options get to be almost limitless.) This kind of combo results in products that aren't so heavy, hard or plain old bean tasting.
Truly I'm still learning on all this too, but it is becoming easier as I finally gather together a varied assortment of options and cookbooks.