How much money do I need in my account to trade futures?

Trading account balances greatly depend on the initial margin requirement of the product you are looking to trade.

For example, the initial margin (maintenance margin + 10%) for a micro emini S&P contract is currently $1298 (https://www.cmegroup.com/markets/equities/sp/micro-e-mini-sandp-500.margins.html).

This means that if you were to buy 1 MES and hold it overnight you would need to have at least $1300 in your trading account to hold it overnight and not be on margin call (presuming the mark-to-market at settlement was favorable).

Intraday margins are usually less than overnight initial margin but vary by broker and product.