2004 mini cooper oil change?

A friend of mine has a 2004 mini cooper S, she takes it in for an oil change every 15,000 miles. Spends over $100 just for oa simple oil change. So i told her i can do this oil change for no more than $30 so i went to auto zone got 5 quarts of 5W40 sentetic, she used a 5W30 sentetic, but then the car is at 80,000 miles so i recomended 5W30 castrol. I did some research as far as how much oil the car needs the socket size for the oil filter cause its a bit diffrent from my 2001 crown vic. The only thing i need to know is when iam about to unscrew the oil filter wheres the oil gona leak to, if its gona leak at all. Or can i just unscrew the cap off and it will not leak? and the second thing i need to know is where in the world is that trop om (TB)? i need to know where its at so i can restart the service oil mileage countdown.