The milky coolant is a bad sign and often indicates a bad head gasket. Do you see any bubbling in the overflow tank when the engine is running? Maybe they did the head gasket repair but didn't do it properly?
Your idle sounds completely normal.
That's good it's not overheating, maybe you can drive it for a while until it becomes a problem. Definitely keep an eye on it, as I'm sure you are.
An oil leak could be from the cam seals, crank seal, valve cover gasket, oil separator plate, oil pan plug crush washer, or the rear main seal (pretty rare). I'd replace the valve covers and see if that helps first. You can power wash the bottom of the engine and then add some oil UV additive and then shine a black light and pinpoint the leak that way.