The order of operations that actually works for building a SaaS product — and why building for scale before you have customers is usually a mistake.
The smallest version that lets a real user accomplish the core task is the right starting point — everything else can wait until you know people actually want it.
Multi-tenant data isolation should be designed in from day one even with one customer, because retrofitting it later means touching almost every part of the system.
Flat subscriptions are simplest. Usage-based or credit-based billing fits products where cost genuinely scales with usage. Add billing once you have users willing to pay.
The first scaling pain points are rarely about raw traffic — they're usually background jobs piling up or a query that was fine at 10 users and isn't at 10,000.
MVP to validate the idea, multi-tenant architecture from day one, billing added once there's real demand, and performance work added reactively as bottlenecks appear.