Five things, in this order: a Cfx.re license key (free from the Cfx.re Portal at portal.cfx.re, which replaced the old Keymaster in late 2025; required even for a local test server), somewhere to run (local for testing, VPS for real players), txAdmin as your control panel (ships bundled inside the FXServer artifact since 2020 and launches automatically on first boot), a framework decision (ESX, QBCore, or Qbox), and a database (MariaDB + oxmysql is the 2026 standard).
What you do not need before launch: a custom MLO pack, 40 paid scripts, or a full custom UI. Every week spent on content before the core loop works is a week your launch slips.