Dart project structure for apps (not libs)
1)
- your_app_package/web
- your_app_package/web/src/xxx
static content like jpg, css go to* your_app_package/asset
2) the packages directory is maintained automatically. You configure in the file pubspec.yaml which 3rd party libraries you want to use and then call pub get or pub upgrade and the packages directory is updated automatically (the Darteditor does this automatically when you update pubspec.yaml).
3) not that I know of.
I had some problems putting additional classed in the code file of a Polymer element though. But I guess this is just a temporary limitation of Polymer.