What are the codes for the placement distance from windows, doors etc. of the furnace vent pipe, a propane gas line and a water heater vent pipe on the outside of a home? General residential code? State of Michigan code? Are there health codes regarding vent "fumes"?

CGA B149 Installation Codes for propane and natural gas show a minimum distance of 12 inches from the vent terminal to any door or window that can be opened, and if I'm reading it correctly 6 feet from any powered air inlet. I've not found any listing for local codes anywhere online. A licensed plumber could probably tell you off the top of his head what the minimum code is in your area. The obvious intention of the code is to vent the fumes to the outdoors, away from indoor breathable air.

I'm very curious as to why you are asking. Do you think you have an existing vent that is not up to code. or something? If you have a situation you're not comfortable with, there's no reason at all you can't exceed minimum code requirements as long as you stay within the maximum vent pipe length, pipe sizing, and materials recommendations, etc etc.

The codes are based on manufactures requirements. Check with the furnace installation instructions for these locations.
But remember, you must take into consideration your average yearly snow fall. While some areas you can get away with only 12 inches above grade, were your located you may need two feet or more. As each furnace side vent system is not the same as the others. Distance requrements vary slightly.
Simply ask the code office this question and they will give you an answer anyway.
But most likely they will say check with the furnace instructions for minimum distances.