Second Picture the panel should be removed to observe the furnace. The door in the back of the picture, is that a bath? No access there?
Measure the openings to see if there is enough combustion air for furnace and water heater.
First picture opening at top of ceiling, where does it go? Possible fire safety issue.
Agree black line appears to be for a washing machine. Check connections to water heater.
Why is there 3M tape on the exhaust for water heater?
What is behind white panel next to water heater? Is there a jetted tub in a bath?
Looks like there is a bar to hang clothes, I would not store clothing adjacent to a gas water heater.
No pan for the water heater.
Carpet in closet I would not put carpet in there.