To implement the strategy in the most tax efficient manner without leverage you would want to have an account worth 5 * (S&P 500 futures price). Today that would be about $26,375. MES uses a multiple of 5 while ES uses a multiple of 10.
However, with today's $0 commissions, if you aren't overly concerned about taxes, you can try out this strategy with as little as $500 and simply buy and sell one share of the ETF VOO on signal changes. Alternatively, if you have the risk appetite, you can get started with trading MES futures with less than $10k, though caution should always be warranted when using any amount of leverage.
However, with today's $0 commissions, if you aren't overly concerned about taxes, you can try out this strategy with as little as $500 and simply buy and sell one share of the ETF VOO on signal changes. Alternatively, if you have the risk appetite, you can get started with trading MES futures with less than $10k, though caution should always be warranted when using any amount of leverage.