An Expert Adviser - automatic trailing stop for my discretionary system

Hello,

I need to build an automatic trailing stop for my discretionary system.

I will activate it only after I have entered the position myself, manually.

the trailing stop rule is very simple - when I am long FX pair:

if candle closes below moving average, then set the stop loss at the low of that candle.  

as such, the stop loss is always the low of the last candle to close below the said moving average. 

(vice versa if I am short)

Parameters I will have to specify will be:

- the pair eg. eurusd

- the amount to be bought/sold eg. 250k (i am not using lots as units)

- moving average period eg. 5 period MA

- i guess I will have to specify if that is a buy or sell too?

- the time frame I trade is 1 day or 4 H , does this needs to be specified? or EA will work on any time-frame?

Importantly, when the stop loss is actually executed (triggered), then the Expert Advisor should stop working (my aim is to simply close an existing position while I am away from PC).

Thank you

Alex