Position sizing is the most underrated algo parameter. A fixed fractional model (risk 1-2% per trade) dramatically outperforms fixed-lot over the long run because it compounds wins and limits ruin on losing streaks.
Correlation risk is invisible until it hits. If your 'diversified' portfolio of 5 pairs all have >0.7 correlation, a strong USD move will slam all 5 simultaneously. Check correlations weekly.
Store your EA inputs in a .set file and version-control it alongside your MQL5 code. When you tweak parameters, save a new .set with the date. You'll thank yourself when you need to roll back. Full breakdown in my trading toolkit → https://t.co/5wudBU7CIq