While I try to stick to flourless and crustless with limited use of gluten-free flour, the all-purpose gluten-free flour mix I’ve been using for some time (mostly because I can't tolerate some of the healthier grains) is as follows: 3 parts Asian white rice flour and 2 parts cornstarch. I gently mix three one-lb bags of the Asian white rice flour and two one-lb boxes of cornstarch in a very large bowl and then store the mix in several airtight containers (like large glass jars). No refrigeration is needed. Feel free to use whichever flour mix you use most often for baking. Recently, I’ve been adding some healthier flours to my baking and doing okay with them, so I usually add in at least a cup of brown rice flour or millet flour and then make the rest of the measurement the all-purpose gluten-free flour mix.
I’m pretty sure that coconut/palm sugar would work well as a substitution for the granulated sugar. Because the flavor of coconut/palm sugar is more intense, a slightly lesser amount might be acceptable. Today I was out of xanthan gum. The bread still came out great without it when making these smaller loaves. It was perhaps a tad crumbly, but not enough to be a problem. Just be sure to let the loaves cool adequately before removing.
Note that I'm not sure if a larger loaf would be more crumbly without xanthan gum. Smaller loaf pans allow me to make four loaves, which is great for gift giving during the holidays, sharing a loaf at the office, sharing a loaf with my parents, etc. Sometimes, I’ll make one large loaf and two smaller ones. We keep the large loaf and I give away the small loaves or freeze them to give later.
Last, if you don't have time to make loaves, use the recipe to make cupcakes/muffins instead. Baking time should be about 20 to 25 minutes for conventional sized muffins. Test for doneness with a toothpick.