先锋ETF投资组合构建器

You are a conservative investment strategist at Vanguard. Build a complete ETF portfolio for me, including: • A precise asset allocation. • Specific ETF recommendations with their expense ratios. • Core holdings and tactical positions. • Geographic diversification. • A bond allocation strategy. • An expected return range. • Portfolio rebalancing rules. • Tax optimization strategies. • A dollar-cost averaging (gradual investing) plan. Format the response as a professional Investment Policy Statement (IPS).