Your proposed dates fall right after the
D23 Expo (Disney's all things Disney Con). I would think that many attendees will try to extend their dates to visit SWGE, adding to the crowds already planning on visiting before school starts. Not all school districts will be back in session by the end of August. And the historic AP calendar has the lowest passes unblocked by the third week of August, so that will add to the crowds, too, as passholders rush back to see their beloved parks after being blocked out for most of the summer. (Changes to the pass calendar are afoot, so this may or may not hold true for next year.) All this to say that I think you are being very optimistic to think that crowd levels will be "not as chaotic" only 2 months after the projected opening of SWGE -- assuming they open on time. If they open late, it won't even be two months by the time of your visit.
I wouldn't let that stop you from visiting DLR, though. With plenty of time to plan and organize, you can still have a great visit. Would it be possible for you to do 5 days instead of 3? 5 day park hoppers would help you to have the more leisurely trip you're looking for, especially with the crowd factor. Be aware that it is possible that DLR will be on the low season/non-peak schedule by the last week of August, meaning shorter hours, lower staffing, and nighttime entertainment on weekends only (Fri., Sat., Sun.). So if you want to see fireworks and F!, it would be better to plan on including one or two weekend nights. Also, HM will probably be down for the Halloween overlay by that time.