If you think you can run a business with 10 high-skilled employees on $40,000 of revenue per month, boy, have I got news for you :-)
Similarly, if you think 1000 B2B SaaS subscriptions is an easy-to-achieve number, I'd wager a bet you haven't run a B2B SaaS business.
Roughly, the calculation is: at $40/month, a single subscription brings in $480/year. That means you can safely afford to spend roughly one hour of support on a subscription PER YEAR. If you spend more than 2h, you are definitely in the red. And you will get support requests, of all kinds: the ones you expect, and then all the stuff about lost passwords, inability to log in, network problems, lost invoices, requests to change the billing period, requests for invoices from last year for a customer that has since canceled and been deleted, data export/import, etc.
People who haven't run a business routinely underestimate the costs of running a business and imagine that these numbers mean that business owners are buying yachts and private jets. People who have run a business realize that it's much more difficult to make ends meet than it seems.