When you talk about how many Bitcoin one need to have before retirement is like you saying you need to a certain amount of money before retiring. Like can you stop yourself from making money if you see the means of getting it non-stop?
To me I don't think there's a cash out plan on this, is really tempting to quit making cash, even if you retire there's a possibility that you might handle things to someone you trust. If I have let's say 2.5 BTC I don't think it would make me retire and I can't stop making it go higher.