Good questions here! I believe they will be useful to others as well.
The first thing I see with your broker is that the spread for GBPUSD is 30 points, which is way too much. You generated the strategies with the MetaTrader-Demo data which is coming from JFD broker and there the spread is below 10. I think this is the main reason you see this result.
Second, you have just 12 000 bars with your broker which won’t be enough to backtest EAs or generate new ones. Did you press the home key to load more bars?
The best thing you can do is to generate the strategies using your broker’s data.
Anyway, if you want to optimize it, you just use the Optimizer or the Normalizer.
Using round numbers will keep you away from over-optimization, but you better use Monte Carlo as well.