If i had sex after urinating and showering, how much sperm would be in my precum. since urinating washes away/kills sperm wouldn't this mean almost none? thankyou to anyone who replies.

You are correct: First, nobody knows how much sperm is in one person's precum at one particular moment. That means if that person is worried about such things, he should use contraception of the kind that gets rid of any such worry... such as using a condom all the time, which completely takes away any precum issue.

Can't tell: You can't tell how many sperm are in the fluid you secrete before orgasm unless you get a count, but there can be sperm in that fluid.