Do I have to journal every scalp?

Yes, or the sample is biased towards the trades you remember. Automatic MT5 import removes the effort argument entirely.

How many scalps before the data means anything?

At least 100 per session window, because the win rate needed for a small-target strategy only stabilises with volume.

Journaling Gold Scalps (XAUUSD)

Journalling XAUUSD scalps requires per-trade capture of the session window in UTC, range high and low, range width in dollars and versus ATR, rejection count, sweep size, spread at entry, commission, and net result after costs.

Reviews group scalps by session window and range-width bucket to find which window pays after costs. The free GoldHunts gold trade journal imports these fields from MT5 automatically.