In my experience...
1. Not true if you own the object. True if accessed via Other Users node, even with privileges. Of course, ability to view code should depend on your privileges.
2. Not true. Check these settings: Tools > Preferences > Code Editor, then any of Display | Caret Behavior | PL/SQL Syntax Colors. Also, double-click gets cell editor.
3. Not sure for all languages/keyboards, but this does sound vaguely familiar. Searching the forum may turn up a previous mention.
4. Sounds familiar. Probably already bugged. Searching the forum may turn up a previous mention.
5. Sounds familiar. Not sure if bugged, but for 4.1 object look-up processing for Popup Describe and Open Declaration seem to have merged, so possibly other fixes (either planned development or driven by QA testing) will get this fixed.
If any of these turn out to be a major annoyance in your environment with no workarounds, it's always best to log a Service Request with Oracle Support.
SQL Developer Team