Welcome to the community, @Mike_Boehm.
While Airtable can be used for all of that, it’s not necessarily “simple”.
Like you said, Airtable is designed to be used in lots of different ways, so you would have to custom-build your entire system from scratch the way you would like it to operate. You could start by using one of Airtable’s templates, but Airtable is not really setup like a traditional ordering system. And Airtable doesn’t really have any sort of a built-in reporting feature such as a cash flow report. You would need to handcraft everything the way that you would like it to work. On the more positive side, Airtable can be integrated with thousands of different external websites & apps, and perhaps some of Airtable’s built-in apps would fill some of your needs as well.
You might be potentially better served by looking for an online invoicing & ordering & inventory & reporting system that is already 100% setup for you — perhaps even Square, which offers all of that for free.
But Airtable can be a powerful & customizable tool that goes beyond what Square can do.