Fee for EACH company file?
I will be doing bookkeeping at home for several businesses. Am I understanding it right that if I use QuickBooks Online, I would have to pay a fee for EACH business (in other words each company file that I use)?
I will be doing bookkeeping at home for several businesses. Am I understanding it right that if I use QuickBooks Online, I would have to pay a fee for EACH business (in other words each company file that I use)?

That is correct. Each file in QuickBooks Online is a separate company subscription.