you can create a datasource as xml...really easy to do
the name of the formulas is immaterial. CR executes the formula in whatever section to drop it in. What 'matters' is the name of the variable. No formal declaration is needed, whichever Shared xxxVar that CR sees first is the declaration, it defaults to 0 for numbers if they are not explicitly set...or reset as the case may be.
Actually each Punch in or out would have its own formula to display its own value (this way they line up all nicely). As for punches that are not used, you could suppress them or display an empty string "", and nothing will be displayed, it's really the same as displaying fields, just you are treating your formula as a field.
As for suppression, it's not needed. I rarely suppress a section just because there is a formula in it. I tend to hide the formula by ending it with a "", since CR displays the last line in the formula.
Hope this clears up some of the confusion. Variables and formulas make CR so much easier / more robust to deal with.