Had almost the same experience. Someone came to us asking if we could build an app, but wasn’t willing to pay full price. We decided to do it for a minimal fee, but under the condition that they’d keep paying a monthly fee per user, and now here we are with a b2b SaaS product and a few more paying customers (it’s been passive income next to my day job for the last few years, revenue allows us to buy new laptops every year, not new cars :)

On doing things manually: i send invoices once per year by hand (few hours of work), do accounting in ledger for 1h once a quarter, and handle uncommon requests directly in the DB (rails console is amazing for that, this happens about once a month), but have automated password resets as we were getting too many emails on those.