Very perceptive ha, yes new here but not new Trailing stops are easy enough using the OrderModify function. You can look at the open and close of previous candles using the iOpen and iClose functions. What you want is not so difficult and there ...

'I dunno if it's possible but to enter the lot size based on the account size, say 1%' yes this is simple and there are EAs on the net which have this in. Maybe doing a Google/Yahoo search will find them. 'and based on a rough estimate of the SL?' ...

There are many MA cross EAs on the net (you even get one included with MT4). Do you have a specific programming question about them?