The Haxe port of Starling is line-to-line comparable to the AS3 version, so a file comparison (except for an extra indent) is mostly semantic differences. Otherwise it is a few fixes for behavior.
If the core team for Starling were interested, it could be written to not require OpenFL, but to use Lime (our cross-platform) directly, but this would mean that projects rely on both Flash and Starling APIs would not port over. Upsides and downsides.
Our intention is not to rewrite Starling.
Yes, we have a port of the latest (I believe) version of AS3 DragonBones runtime. There is a tween library called Actuate that is well tested for Haxe project, or there may be a more recent port of TweenLite. I see one here (https://github.com/theRemix/TweenLiteHaXe) but it might require a little work as it’s designed for Haxe version. I’m not aware of a GAF port for Haxe, but it could be done. Is their runtime open-source?
Yes, you should be able to use Starling and OpenFL display objects together