FCMs want to see at least $500K for WH Bal Day. Ercot is a completely different beast, and the FCMs have the ability to separate ERCOT limits from East Power Limits. ERCOT was in the east power bucket few years back, which meant if you could trade on peak east power, you could trade on peak ERCOT as well. ICE changed that (rightfully so) at some point. Ice margins for a 1 lot of WH Bal Day (Product code "PDP" are currently $26~K. It's up to you to negotiate with your IB/FCM regarding limits on a $500K account. IME it's not like retail futures at all. The FCM will give you more rope than you need to make things work (assuming someone can vouch for you). I always requested liberal limits even though I never came anywhere close to reaching the limits.
One of my mentors was David Ellis - a legend in the S&P pit. One of the tenets he personally impressed upon me was market price behavior flying in the face of "conventional wisdom" and the espoused views of "expert commentators". The S&P 500 is currently a great example of what he was talking about. The market price action itself has remained strong despite the widespread commentary about the market being overbought. I suspect David would view this as a bullish sign.