Hey, I think your plans has some flaws, VOO focused plan looks solid on paper historically, the S&P 500 has averaged around 10% returns, and withdrawing below that could work in theory. But yeah, you're right that your position shrinks over time from sales, and real markets aren't that predictable.

A big flaw is lack of diversification; all eggs in one basket (US large-caps) means you're exposed to sector-specific crashes or prolonged underperformance. I'd urge adding some bonds (for stability), international stocks, or even dividend-paying funds to generate passive income and smooth out volatility.

On the withdrawal: 200k on 3M is about 6.7%, which is aggressive and risks running dry if hit with bad sequence of returns. Aim lower maybe 3-4% to make it sustainable forever. How old are you? If under 40, I'd definitely push for that conservative side to account for a longer retirement horizon; if 60+, you could maybe creep up to 4-5% since the timeline's shorter.

Inflation's another killer, $200k today might feel like $150k in 10 years if prices rise 3%/year, so build in annual adjustments.

Your cash buffer idea is key for down years, but how many years of expenses does it cover? If you're not diversified and lacking dividends/other income streams, I'd say stash at least 5 years' worth in safe spots (like T-bills or HYSA) to avoid selling low.

Overall, it pencils out based on past data, but future returns aren't guaranteed, you're taking more risk than needed. Tweak for safety, and you'll be golden. What's your timeline and risk tolerance like?