What slippage to use at my EA?

What max slippage should i put to the OrderClose and OrderSend functions on 1 or 5 min timeframes to my EA, basically to EUR/USD or GBP/USD or any other volatile or not volatile pairs , on ECN broker?

Are the TP and SL levels also affected by the slippage, so that it will close outside them if the slipapge is big [B]or[/B] it is guaranteed and only the OrderClose and OrderSend functions are affected by the slippage