warlad,
the market depth is not yet available on the java version. it should be available soon. on tws 3.0 order depth is available.
andrasm,
E-Mini S&P 500 (ES) current margin is $4,313 and maint margin is $3,450.
E-Mini Nasdaq-100 (NQ) current margin is $6,750 with maintenance at $5,400.
In the end how much you need to put in above the initial margin probably depends on how disciplined you'd be in cutting losses and how bothered you'll be if you get liquidated in the event of a sudden move. As long as you're closing out positions each day and thus are not subject to overnight risk, initial margin should be enough under normal circumstances. However, with the current volatility and swift moves, that may not be enough. IB requires 6575 to open a futures only account, and 20K for a futures/options account.
BTW, if any of you are looking for a fairly volatile market to trade after US hours you may want to look at the HSI (Hong Kong) futures.