As you've said at the moment default values are at the project level only.
You can write a Gemini plugin that will listen to the relevant event (issue create, issue assigned, status changed etc...) and update the assign to to your choice using the web services. This is very simple to do.
The same applies to the status movement. Unless you've ment that you'd like an email alert...
To change which fields are visible during issue creation please amend the relevant field visibility scheme (Administration -> Field Visibility Schemes). Note that the scheme applies per issue type.