Do I file extra income in one place or two? For ex: I've posted it in "other employ. income" but do I need to put it also in the "reconciliation of 2017 business income"?

"Reconciliation of 2017 business income" is only used if you have a business, and that business doesn't use a calendar year (January 1 to December 31) as it's tax year.

If you have employment income but no slips, then you would only need to put it in Other Employment Income.