HELP! I bought a mess?

1st question...... if it’s together and running now...... why do you have to change anything?
Smoking. Everything leaks, BAD. Most disturbing is there is an unmixed coolant leak at the back passenger side of the motor running down the scatter shield on the trans that I can confirm is not coming from the head so must be coming from one of the freeze plugs on the back of the motor under the auto trans bell.