After 3 days, guests and fish stink.
While you are feeling out this new arrangement, limit your maximum days.
If you get someone you just don't like in your space, you may stop forever.
As for your pool, it is up to you to charge or not. Just make it upfront.
If you choose to advertise it in your listing, say "Available for a small charge"
Put this on your pictures of the pool also.
As for your bathroom situation. It is what it is. Do not apologize or deviate from your normal usage.
I would limit kitchen privileges to microwave and reefer. I get uncomfortable when people cook in my kitchen. It works out, cuz most guests don't want to cook.