Standard Risk per trade should be 2%. this is how most successful traders do & follow.
There is only one successful trading strategy, that is MONEY MANAGEMENT. No other trading systems or indicators work efficiently for a long term.
Though EurUsd is on the downtrend, going short position is prone to risk since euros is trading year low and breaching this level could lead euros to historic low. I would rather wait for a trend reversal signal instead of selling at this point.