Import employee master in dynamics ax 2012

hello,

I have three questions in my mind now:

1.how do we import the employee master in ax using excel, and the condition here is that i've got a many sheets in the excel file.

2.The sheets in the excel have both employee as well as contractor details, so my question here is do i have to import both employee and contractor at one time or separately.

3.when do we exactly import a master say employee master, i.e, after the basic setups are done or after doing the customisations.

Thanks in advance