I'm no lawyer so this is a just what I would surmise:
It is a long term (6 month) lease, so you can't limit occupancy like a hotel can. You are going to be subject to occupancy rules for regular housing.
You can usually limit occupancy to two to a bedroom unless the bedrooms are very large in which case you may be required to allow more.
You probably legally cannot restrict your renters ability to have guests over, and doing so would also probably hurt your chances at renting.
You can restrict how long guests can stay, but your issue is really how many people are staying there.
As long as your 8 person limit complies with the law (ie it is not a 5 bedroom house), you could amend your sentence to read: "The number of people staying at the residence overnight, including guests, is not to exceed 8. In the event Landlord finds a violation of this lease term, there will be a $75/night charge for each person over the 8 person limit."
Now the real question is, how are you going to enforce this? Knock on their door at night and do a head count? And what is the real problem?
If it is wear & tear on the unit, give them a warning on a weekend where there are more cars, and then if it continues raise the rent next lease term.
If the issue is the number of cars, just limit that in the lease.
If the issue is safety, get the fire marshal to come with you to do a head count. --74.232.xxx.xxx