All the previous posts are very good imo.
One piece of caution, very, very important and easy to forget :
Optimize as little as possible.
It is tempting to adjust all your parameters to get the biggest.. whatever (perf, R ratio etc..).
You mention stability so I guess you are aware of the pitfall.. nevertheless I'd add extra emphasis.
Optimizing on past data is counter productive and possibly dangerous.
It is better to keep the system simple and sound : ie explain to yourself the rational. Or why should it work ?
Retracement in a trend is rational. In this case your goal (as usual) is to control how much you loose for how much you win and that to me is the most important ratio. forget all the rest if expectancy is not there.
Drawdowns and flat periods are very good points from earlier posts too. But only as a measure of what you must expect to stomach (and eventually forget about the system if you can't take the heat).
Optimizing more will drive you in losses, that's the system trading paradox.
A better way : try your system on several DIFFERENT markets at different point in time. Then try forward testing, aka simulation.
Consider slippage, and make it bigger if your time frame is smaller or your size bigger (size does matter

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