Be careful with ‘bien fait’. You may think you are saying ‘well done’ but the expression ‘c’est bien fait pour lui’ translates as ‘serve him right’. Don’t say it if you see someone nearly slip and then right themselves on a flight of steep steps.
‘Pas mal’ translates as ‘not bad’ but ‘pas mal de …’ translates as ‘lots of, many …’. As can often happen, a big difference is made with the addition of one little word.