$40/month per user, just for support? So for 1000 users, you need to make $40,000 to be sustainable, i.e. like 10 employees?
Back in early 2000s I ran a shared webhosting business, most customer's were savvy at the time and it was kind of a "you're on your own, let me know if the infra is acting up" type arrangement. I ran it with about 2000 customers for a year or so solo and only got about 2 support emails a day. Back then, 24-72 hour response was acceptable so I never needed to be a 24/7 resource.
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.