How do you use AI to operate at the scale of a 20-person company with a team of 4?

I'm building a B2B SaaS with my co-founder and one engineer. Our competitors have 15–20 person teams with dedicated marketing, sales, CS, and finance functions. We need to punch above our weight. I've read the advice about "AI as a force multiplier" but I'm looking for specific, worked examples of how founders at similar stages have actually structured their operations around AI to avoid the hires they can't afford yet. What's working in practice?