There's no reason to mess with the thermostat unless you want to. Change the pump, change the coolant, new oil and filter would be good and ride her.
I found out about the water pump holding the oil in place the hard way also. Way back in 01 or 02 when Prestone coolant did not list silicants in the ingredients, my water pump went.
My dealer warranted it, but I changed it, hence the oil on the shop floor.
