What is a good expectancy per trade?

Anything reliably above 0.2R across 100 or more trades is a workable edge.

What win rate do I need with 2R winners?

33.3% to break even if losers average 1R, so a 45% win rate carries 11.7 points of edge.

Expectancy is the average result of the next trade in R; profit factor is gross winnings divided by gross losses across the sample.

Almost always because the average loser exceeds 1R through widened stops and slippage around 13:30 UTC data.

Expectancy is win rate multiplied by the average winner minus loss rate multiplied by the average loser, both in R.

A 45% win rate with 2R winners and 1R losers is 0.35R per trade, or 35R across 100 trades.