Bare minimum I’d say genuflect upon entering your pew and when leaving at the end of Mass.
Maximum I’d say genuflect everytime you leave or enter the pew, even if you’re just leaving to go to the back of the Church.
I would say cross yourself with the holy water when you enter the nave the first time and when you leave the nave a final time.
I have been told, however, that you need only cross yourself with holy water upon arriving because you receive a blessing at the end of Mass so have no need to bless again but I see everyone blessing as they leave as well and I’m quite sure blessing yourself twice isn’t an issue unless you’re doing it for superstitious reasons.
As a side note, when you enter the pew, kneel and pray.
For a long time, as a convert, I was entering pew and just sitting and reading the readings for the morning but eventually the priest scolded me for it and encouraged me to kneel upon entering as I was in the presence of the King.