1) Starling is great at performance, but only in GPU(mobile)/CPU(desktops) mode with Animate CC you have an unprecedently and unbelievingly fast workflow, that there's nothing to compare to.
Starling workflow is decent, but I would prefer Godot or something similar because of a mature feature-rich editor. Though, when almost everything is done via code (like with Starling), it's easier to merge changes, when you're in a team.
2) Definitely not what I would advice as a reason to learn Flash. It's best to use tools that ease and fasten your work, otherwise you most likely will never finish your project.
4) Spine dropped Flash/Starling runtime, so you can only use older one, but not the newest features. I guess it's OK for now, until Spine will release something new and revolutionary, especially as Spine has a very convenient way to downgrade installed version with a single click, so that's more of a future/support concern, rather than a current problem.
Animate CC -> Flump -> Starling worked fine, though those are outdated tools.
5) For games, Animate CC is amazing. It's not free, though. Additionally, modern technologies UI is moving towards XML-like declarative scalable UI, so Animate (and Feathers?) do not look that modern and might have problems when your app is both on mobile and desktop, but it works fine enough to do the job.
7) Air handled mobile camera without extensions ten years ago, did not try recently.
8) Only Animate CC / DisplayList has precise HitTest, but it's performance costly, so I believe, Flash/AIR lacks precise and performant collisions checks. Check by distance/radius works fine most of the times, but we have another sad bottleneck here - ActionScript performance is very slow, even comparing to JavaScipt, as Google optimized V8 very smartly. So for small amount of hittest checks - fine, for many objects simultaniously - relatively awful.
I tried to create an RTS in AIR with using only circle colliding (manually calculating distance based on radius, avoiding square roots) - with 50 units checking collisions with each of themselves each frame in a single thread (no Inlines), my Ryzen5 was not enough for decent FPS.
14) Present in AIR itself, but not easy/quick to implement. Used Sony Dualshock 4 with Windows 10 and MacOS for not a final project, worked flawlessly, but picking direction bindings was a mess. Windows and MacOS send different directions, but that's fixable. Never tried on mobiles. Would be nice to have an extension, and not to code and test all by yourself. Gyroscope code looked strangely complicated/inconvenient to enable, so I did not check it.
17) Android seemed to have big latency, but that's not the AIR problem.
19) Sockets encryption is used from your operating system, so new TLS should be working. Unencrypted sockets work fine, I've connected my C# console app with AIR. WebSockets support (with modern encryption) might be a big issue, not sure here. REST API works flawlessly.
22) Starling performance is amazing. GPU performance seems to be amazing until too much graphics to auto-fit into one atlas. ActionScript performance is bad relatively to other modern technologies. But for an average game, when not too much calculations/collisions used, it's definitely performant enough and nothing to worry about, even on mobile.
23) I would emphasize on modern IDEs/editors, not FlashDevelop. Older Intellij IDEA work fantastic. Did not try Visual Studio Code, but that would be my newbie pick if I would learn Flash nowadays.
xx) Language: AnctionScript 3 - very decent, laconic. Very like Typescript, so you can re-use your experience and easily switch between them. Way more convenient and easy to understand what internally is going on than with Typescript, but does not have many modern quality-of-life things (yet, as it seems to be planned in the far future).
I would emphasize on ActionScript and TypeScript similarity as one of the best convenience to learn AIR. As an example, strange language for me (Lua), with which you can't easily use your experience in a job market, was the only reason why I avoided learning Defold.
yy) Debug: with Intellij-IDEA compiling approach, debug process is amazing, way better for me than in Unity or .NET.
zz) Live reload: no, not yet
aa) Continuous Integration / Delivery / their ease of setup : bad???