If you save as a flat file (csv/txt), you can use a schema.ini file to specify data types, which ArcGIS will honor. This is something that is created automatically when you open a flat file in ArcGIS; here's more info for you to consult:
Schema.ini File (Text File Driver)
You can edit the schema.ini driver file with a text edit (right click, edit with notepad if it doesn't open with a text editor on double-click). Make sure the .ini file is in the same directory as your flat file.
Regarding you zero division error, you can fix this in Excel before saving as a flat file:
Correct a #DIV/0! error - Excel
It's basically an inline if statement, something like:
=IF(A2=0,"",A1/A2)
This would probably even fix the issue with using Excel as the source in ArcGIS, so it would be recognized as a double.
Also, worst case scenario, you could you could copy your column with division errors, then right click an Excel column, then "paste special", then choose "value only" - this should allow you to find/replace the division error values and replace with null.