You are over-thinking this.
Markets change. Each currency pair is different. Each person’s psychology is different.
That last one is a really big deal. You are building a strategy that takes a string of small losses and the periodic big win. That’s a perfectly valid strategy, but I would hate that. Give me smaller, more consistent wins any day. That doesn’t mean that my plan will necessarily be more profitable than yours, but I’m much more likely follow a strategy that fits my psychology.
Constantly tweaking and adjusting a recurring trade plan to fit your psychology, your circumstances, and the instruments you trade is exactly the approach you should be taking.
My suggestion is that you start forward-testing; it is actually fairly easy to come up with a profitable trading plan with historical data. Implementing that plan in real-time is much harder, and will show you the holes in your plan in a way that back-testing won’t.