1. Neither the original create.swf or my extended create.swf are active projects. The original hasn't been updated since 2015 and KirbyM has been working on other projects and doesn't seem interested in create.swf or Touhou in general. As for my project, I had a hard drive failure and lost months of work on the project, add on top of that being burnt out with the project, I haven't had much desire to catch up my old code back up-to-date.
2. Unfortunately no, I tried to import some characters made by some people but flash is super finicky and ruins just about everything that didn't come explicitly from flash professional itself.
3. Select a character and press V.
4. Select a character, open the prop menu->detach->arms.
5. You can look through the createX manual
it goes over the new features.