1. No, there is no conditional method of merging data. What you could do is create templates for the various scenarios, breakout your data accordingly, and do multiple merges.
2. You can do multiple record (step and repeat) merges one side only. You did not say whether the back side is common or variable. Regardless of back side, I would recommend accomplishing the merge first, imposition second.
I think that reponse was maybe misleading. Data Merge CAN delete empty lines, so if the only thing on a line is a field or fields, no white spaces or punctuation or other text, then those lines can be deleted automatically during the merge. Does that help?
agree with the above two posters -
* indesign can't "conditionally" merge - it just takes data from a txt/csv file and populates it where the fields were placed.
* indesign CAN remove blank lines. when performing the merge, go to the data merge flyout and select "content placement options" and in the new dialog box, check the box which says "remove blank lines for empty fields"
depending on WHO is printing the business cards (e.g. the OP on their own printer or a commercial printer on a copier or press) determines whether i'd put the cards up together to print (i.e. a printer's imposition). if the OP is printing the cards on their own copier, fine - this is done from the "create merged documen" OR "export to pdf" options from the data merge flyout. in the first tab of the dialog box, there is an option which appears for multiple records which needs to be checked. this allows the second tab to be visible and then shows how to prepare the cards.
"the indesigner" - Michael Murphy - has some videos on his own blog which may help - http://www.theindesigner.com/blog/category/automation
If the OP is sending out finished art to a copy shop or press, i'd supply one card to a page PDFs as it is up to the print shop/press to know how many cards they will need on a sheet, and preparing an imposed file will only waste their time as they will have to "unimpose" the cards manually to suit their own needs.
I think that reponse was maybe misleading.
Right, that is misleading after rereading the OP's question.
To clarify, Indesign datamerge could do this:
This person does not have a cell number, and the fax and email moves up a line.
Indesign datamerge can't do this:
This person wants their cell above the phone, and the variable placeholders are in a different order.
Right. You can remove blank lines, but you cannot change the order in which things appear.
Thanks for the excellent illustration.