They can't let the animal annoy the neighbors by barking all day, urinate on the walls, or chew up the window sills.

The previous owners took reservations mostly by phone, wrote them on a big paper wall calendar and hand keyed CC numbers into a terminal 😲The bunk beds have been a huge win. 

You could build a block wall like they do on freeways, but why put a bunch of money into the place?

$40,000 x 25%(assuming a 25% interest rate on credit cards) = $10,000This is more than the annual cash-flow that you are getting from the rental.I would look at a way to paying off the credit card debt asap.Look to see if you can take a HELOC on the investment property(likely difficult).If you can't you may want to consider selling the proprety.You will also feel a lot of relief of not having credit card debt hanging over you.What is the interest rate on the car loan?

Stop hanging out with your deadbeat buddies who spend all day drinking, talking sports, and otherwise wasting away.

If I change things (new sleeper sofa, new pictures on walls, different bedroom furniture) I change my pictures

Well, unless we want to go at it from the legal end, which wouldn't be worth it in our case...If the wardrobe (think cheapo ikea) is fixed to the wall, the appraisers we have used consider that "Builtin" YMMV

No grey LVP flooring or walls.

If it is an older home with stone foundation and brick/block walls likely you will need to underpin the foundation while lifting the home and then star bolting any active bulging. 

These guys operate like flies on the wall.