From my experience as a scalper :
Lots 0
Risk 3-4%
Max 2-3 ( 2-3 trades a day are enough to protect your capital aswell )
SL 250
TP 500
Trailing stop starts at 300 ( avoid getting stopped out by retracements that happens a lot in a market like AUD/USD)
Trailing step at 100
Bull 3
Bearish 5
==> run these settings during NY session or Asian session to catch bigger moves