I'm a Millennial and I agree with all these points except the 3 day rule, which can be broken if known about in advance (I'm going to be staying at my best friend's house for about 10 days over the summer).

I would also add:

- Offer to pay for some meals while you're there (like takeaway, or even a few restaurant meals), not only will I pay for my own food when I stay but I will also pay for some of my friends' food so I am helping to make up for the cost of them hosting me

- don't expect your host to constantly entertain you (while my bestie and I are looking forward to spending lots of time together, I will also be out of the house a lot so he can have private time)