Five numbers cover a small business: leads by source, cost per lead by paid channel, conversion rate of your main page or form, review count/rating trend, and revenue attributed to marketing (even roughly). Everything else is drill-down.
The discipline that makes five numbers powerful is sameness: same definitions, same ruler, every month, written down. Trends surface problems long before any single month's number does.
Skip the vanity aisle entirely, impressions, followers, 'engagement', unless one of the five numbers degrades and you're diagnosing why. Dashboards exist to prompt decisions, not to feel busy.