The stack
Plausible for page-level traffic ($8/month, GDPR-friendly, no cookie banner needed). PostHog free tier for product events and funnels. Stripe's built-in dashboard for revenue. That's it — total under $20/month for the first 10k events/day.
What to track on day one
Five events, max: signup, activation (first real action), key feature used, paid, churned. Five events you actually read beats fifty you ignore. Add more once you have real questions to answer.
What not to use
Google Analytics 4 — slow to load, hostile UX, and a significant share of visitors block it via ad-blockers or tracking-protection browsers (see the eyeo/Adblock Plus usage reports and Brave's blocking defaults). Mixpanel — overkill until you have 10k users. Custom dashboards built in-house — every founder builds one, none of them maintain it.
The one chart that matters early
Activation rate by signup week. Are new users doing the core thing within 7 days? If yes, scale acquisition. If no, fix activation first — every other dashboard is a distraction until that number is right.