Regarding exporting all the expressions, go to the expression overview (CTRL+ALT+E) and click on Export
Regarding setting a default format, you can do it at a field level by going to Document Properties > Number (see below)
Regarding exporting variables, I don't think there is a built in way of doing it; have a look at this document:Export Variables.zip
The solution would require writing macros
The Document Analyzer tool
Qlikview Cookbook: QV Document Analyzer http://qlikviewcookbook.com/recipes/download-info/document-analyzer/
can help you identify unused variables and fields.
You can export expressions and variable from the charts in the tool if you wish.
from Barry Harmsen can also be used to bulk export/import variables from a qvw.