@Lauren522 The long term policy only kicks in for bookings of 28 days or more, you can't choose it yourself for bookings of less than that.
There are many reasons why Airbnb isn't a suitable platform for longer term bookings. There is no real security deposit charged, you really don't know anything about the guest as you would if you operated as a landlord, like getting references, work history, etc.
And as a new host, you should give yourself time to find your way around using Airbnb, learn from other hosts, as you have done by asking these questions, and become adept at vetting guests and knowing what to watch out for as far as red flags.
As well, as a new host, you want to build up as many reviews as possible, which can't happen if you take long bookings.
I would suggest that a new host set a maximum booking period of a week or so. You can always change your settings at any time if you decide to. And no, I wouldn't rent for almost a month to a new user with no reviews.