Normally, 6-8 repair pickups are suggested for a pit lane. Place them roughly in the middle of the lane, with them all running along with what the driver's route through the pit lane. You might also want to place one near the end for good measure as well.
I would only use 3-4 wrenches because most people use a million and it makes it impossible to see anything, especially at night. Also, how many people will be using the PIT lane in the same 1-2 laps? I doubt more than 2. Where you put them depends on the PIT lane you made. I also like to put a sign pointing to the PIT and a wrecked car to show where you can fix it.