Retirement tax questions

OK great, thank you for the extra pair of eyes on the instructions. It's tough to know what can be left blank and what is required. 

 

I actually do have an EIN for one of my Schedule C businesses, as I was required to get one for a sales tax license in one state. But how to tell which business the SEP contribution came from? Safer to just leave blank perhaps? Or does it not matter? The EIN biz had the higher income. 

 

And good call on Schedule A Line 3, I overlooked that in my summary in the post. 

 

One other question I thought of: I only need to file this for just 2018, correct? IRS will work out whatever penalty I owe after I file this? 

 

The form says "Taxes that are reported by the last day of the 7th month after the end of the tax year", which would have been July 31, 2019. I assume the timeframe after that is all about potential additional penalties?

 

Thanks again!