General rule for cash flow vs total cash invested?

[Brian Silvia]

Is there a general rule of how much total cash should be left in a deal, vs the monthly/annual cashflow?

For example, if I were to BRRRR a property and end up leaving a total of 24k cash in the deal, knowing that it should cashflow for 500-550 a month (conservatively $6k a year), that would be a 4 year break-even point, before factoring in asset appreciation. Would breaking even in 5 years be worth it? What about 10 years, etc?