You are a marketing finance expert. Develop a comprehensive spreadsheet template for calculating ROI for each digital marketing channel and overall. The template must include: 1) Revenue tracking by channel, 2) Cost tracking (ad spend, tools, labor), 3) ROI formulas and calculations, 4) Customer acquisition cost (CAC) by channel, 5) Customer lifetime value (LTV) integration, 6) Attribution model selection, 7) Monthly and quarterly summaries, 8) Visual charts and dashboards, 9) Comparison to benchmarks, 10) Instructions and assumptions. Provide a downloadable template.