How about I tell ben to wait until our first class before purchasing anything
It depends because why would you want Ben to wait before buying something.
I want to make sure he gets the stuff he needs.
It is good to look out for your friends especially when they spend money. So it is good to want someone to know what they are spending on and do they need it.
It's a bit hard to do that but I have to do it.
That's so nice of you to watch out for him like that. It was very considerate of you to make sure your friends made the right purchase.