@Bonnie, I'd advise against it. I've read of forum members having this experience, and ending up receiving mail, packages, etc., long - even years - after the guest had left. In addition, you don't know what sorts of things will be arriving. It's your home, not the guest's.
If there's a post office in the vicinity, surely he/she can arrange for a mailbox of his own.
I note you're in California. I believe that's the State where there's a danger of long-term guests (e.g. longer than 30 days) claiming squatters' rights after that period.
Is the guest already in residence? I note this person appears to be your first guest. Do you know anything about him/her? Job? Place of work? Reason for wanting to stay long-term with you? Did he/she have ID verification or reviews when he/she booked?
I also note you have no discount indicated for weekly or monthly rentals. Is this intentional?
You also indicate no charge for an extra guest, though your nightly price is very low for the possiblility of 2 guests. What if your guest decides to have someone staying the night?
The House Rules are also fairly general. I'd recommend making them more specific and comprehensive.