I always create a new external file template with limited number of columns and automate most of columns where the info is not available in the file. E.g. currency, company, or text etc
In my case always there are code parts. At least account and cost center, once imported I am following regular voucher import process.
Check external voucher
Create external voucher
If the external file does not provide payables to employee account info then allow for voucher differences and set the posting control as your employee payable account
Also create a separate load type and voucher type so you can easily track the payroll transactions.