don't even think about trading ES (1-lots) with less than $5K. Technically, you can open an IB account with $2K, and you could put on one ES daytrade, but if you didn't win that first one, you couldn't trade again. IB requires a minimum balance of $2K to open a new position, regardless of instrument (stock, futures, option, etc).
Also, those ES margins of $2K initial and $1.6K maintenance are intraday only. To trade outside of normal market hours or hold overnight requires $4K initial and $3.2K maintenance! :eek: