If the separate businesses are all under common control, say because they are owned only by you, they are considered to be a controlled group and are required to be treated as a single business for the purpose of your SEP plan. Presumably TurboTax used the aggregated profit when calculating your maximum permissible SEP contribution.
As for the EIN, the EIN probably is more relevant with regard to filing Form 5330 for a qualified retirement plan like a 401(k). The instructions indicate to use the same EIN as you would to file Form 5500, but a SEP plan has no requirement to file Form 5500. You can probably just leave it blank.
As far as I can tell, you only need to file this for 2018, but I'm not entirely certain of that. Some lines of Schedule A pertain to applying a previously nondeductible amount to a future year, but it's not entirely clear if that's needed only when you still have a nonzero deductible amount for that future year or if you can just not file it if no previously nondeductible contributions remain. Under Who Must File, the instructions refer to filing when the employer has a liability for one of the excise taxes, so it seems that if you've eliminated the previously nondeductible amount by applying it to 2019, there would be no need to file the form for 2019.
Yes, the last day of 7th month after the end of the tax year is the filing deadline.
