The hour was never the product is a line more service businesses should take seriously, not only those moving into software. Clients rarely want hours. They want a specific problem to stop costing them money, and hourly billing hides that behind a timesheet.
Your point about the existing client list pulling the price down is the one I would watch most closely. People who knew you as an hourly shop will compare the product price to what they used to pay for a few hours, which is the wrong reference. The right comparison is the cost of the problem the product removes.
On seats versus usage, legal teams usually prefer a number they can put in a budget, so a seat price with a generous usage ceiling tends to be easier to approve than pure metering.
I also agree with treating the first customers as a deal nobody else gets. Writing that down as a dated founding offer keeps it from becoming the default.