My husband and I have lived in Briar Chapel for a year and a half. No kids yet, so I'm not qualified to answer those questions, but I can address questions about the community, utilities, etc.
As far as sustainability goes, I'd say the community in general is pretty good about following through with it's "green community" status, BUT you should keep in mind that it is a corporate-owned neighborhood that is trying to make money and maintain nice aesthetics for marketing purposes. With regards to public areas, and areas along the entrance roads, many of us wish they would spend less money (and use fewer resources) maintaining such a groomed appearance... many others want them to do whatever they can to make the neighbor as desirable as possible to increase home sales. I'd say they strike a good balance as most (all?) community areas are watered using recycled gray water, and they pick plants that can survive hot, dry summers, etc. There is plenty of non-groomed forest, and they've done a good job of filling in with new trees some of the areas where the old trees had to be removed.
Quite a few homes have solar panels (way more than you'd see in an average new community), rain barrels, etc. so it appears that the HOA is pretty willing to work with people who want to make their homes "greener." Also, the events they host throughout the year tend to highlight local businesses, and there is a weekly grocery truck that parks in the community lot and brings organic, locally-sourced foods for residents to shop.
With regards to utilities & the "greenness" of homes, we could not be happier! We have a 2500 sq ft Saussy Burbank home and our utilities are lower than they were in the (old) 900 sq ft home we lived in in Charlotte. In the winter our electric bill is about $85-95 per month, in the summer it goes up to $130-160. In the winter our gas bill hits about $90 in the coldest months but is about $12 most of the year. We are not shy about running the heat or the A/C and we both work from home and are here using power all day, so if you were at all more conservative with running it your bills could be MUCH lower. (Tend to heat it to 70 in the winter and cool to 70 in the summer). The house is very well insulated and sealed, including the crawl space. Not sure what our water bills tend to be, but even after planting grass and watering it constantly we didn't see a huge jump.
As far as trees in the yard, most of the lots come with maybe one or two small, young trees in the front. From there, it really depends on what you want to plant. While many people's yards are pretty barren, several of our neighbors have done a really nice job of planting trees/large shrubs for shade & privacy. With a little bit of planning, even small yards can be planted nicely. I think in about 5 years, once the trees have grown in a bit, the neighborhood will look a lot better. I far prefer having a small yard but plenty of access to forested trails rather than having a large yard that I have to maintain... but that's just my preference.
Hope this helps! If you have any more specific questions about the neighborhood, feel free to PM or ask here!