@Melissa717
Long term stays are always charged/paid in monthly installments, so i do not understand why your guest is charged for much more at start of booking. Also it will have the "long term stay" cancellation policy on it.
I personally would not host somebody for such long period, i would change such a guest after a while (i do 10 weeks maximum) to a normal renting contract due to legal reasons. For more info type "long term stay" as keywords in the Airbnb HELP feature,
Best regards,
Emiel