1.) Talk to your best friend about it and see how she feels. If she's okay with it, then you're good to go! If not, then you have to weigh the importance of this guy against the importance of your relationship with your best friend.
2.) This could be an issue in the future, if the two of you are ever in a situation to share funds. For now it shouldn't effect you much. You can help him in this department if it's important to you, maybe help him create and manage his own budget?
3.) Why are his grades important? I don't understand why people put so much emphasis on intelligence. It's nice to be with someone who you know has common sense and isn't going to make any horribly stupid decisions, but isn't the way he treats you and how well you get along so much more important than whether or not he's a brainiac?
4.) You can easily slow this down. Tell him you want to start slow, and make sure he obliges. Start off with seeing him only a limited number of times a week, for a limited amount of time each time. If he pushes for more, politely decline him. If he respects your limits in taking it slow, then that's great! But if he doesn't respect your limits then he doesn't respect you, and it's not a good situation to be in.
So you can let yourself fall for him, but be careful about it. Don't let your feelings get out of control before you know the relationship is ready for it, and make sure you're sensitive to everyone's emotions involved.
Hope this helps you out :-)