How many columns in a table can you specify for auditiing (CFR11)?

I am try to use table auditing (21CFR) fior the first timne and wanted to know the following:

1) How many columns in a table can you specify for auditing?

It seems F9500004\5 will only hold so many audit columns for a table.

2) Does the entire before\after record get written to the AXXXX or Fxxxx_ADT table that was the permanent file.

3) When you disable auditing for a table, does the file name revert back to the previous name it was before it got renaned to AXXXX or FXXXX_ADT?

4) If you only intend to use auditing in Production, is it recommended to setup auditing in DV environment and promote\copy settings to Prod environment?