Hello Andi,
1. Yes it is possible to work on a form in a team environment. We do this here at Qdabra. However, unfortunately it is inadvisable for multiple developers to work on the form simultaneously. Adding controls to a view causes changes to the manifest.xsf file that will be near impossible to merge if more than one person makes changes to it at once.
2. If you intend to have code in your form, create an InfoPath project in Visual Studio and bind this to source control, instead of starting in the InfoPath designer and adding code to it. The former method will create a project with a structure that will allow flexibility with the files' path on the developer's workstation, and it will automatically have the form's source files splayed out instead of packaged in an XSN.
If you don't need code. you can just create a form in InfoPath, extract the form as its source files, and keep these in source control.