water/coolant mixing with oil?

You got a head gasket leading or possibly cracked cylinder head. The engine oil and coolant are mixing together to make it milky looking. The white smoke out the exhaust is from the engine burning the coolant.

what cause oil dipstick and oil cap to look milky, and white smoke coming out of tailpipe?

Yep, AMAILCHECKER01 is correct, this guide can help you see what is going on and confirm the failure.

https://www.2carpros.com/articles/head-gasket-blown-test

and

https://www.2carpros.com/articles/recognizing-the-symptoms-understanding-a-blown-head-gasket-in-your-vehicle

Please go over these guides and get back to us.