Build a Financial Model Assumptions Sheet

I am building a financial model for: [DESCRIBE THE BUSINESS]

Act as a CFO and help me build a comprehensive assumptions sheet.

Business model: [SaaS / e-commerce / services / marketplace / other]
Stage: [pre-revenue / early revenue / scaling]
Planning horizon: [12 / 24 / 36 months]

For each assumption category below, provide:
- The specific assumption and its basis
- A conservative, base, and optimistic scenario value
- The key driver or sensitivity (what makes this assumption go up or down)
- How to validate this assumption with real data

Categories:
1. Revenue drivers (pricing, volume, growth rate, churn)
2. Cost of goods sold / delivery costs
3. Customer acquisition costs by channel
4. Headcount and payroll growth
5. Fixed vs variable operating expenses
6. Working capital requirements
7. Key milestones that change the model

Flag the 3 assumptions that will have the biggest impact on the model's outcome.