My own advice is to wait — at least a couple of weeks to let the excitement ease up. My son got his first offer in the same way and about the same time, from a D2. We liked it and our first instinct was to grab it and run. We were lucky in that the coach making the offer applied some brakes, telling son he would likely get some other, possibly better offers, but he wanted to be one of the first and wanted son to know he was wanted. It was great positive reinforcement in a crazy journey.
If the school is your son's dream school, that's one thing. If not, take a deep breath and try to get past the "what if no one else wants him?' to the "wow, he can do this" phase of recruiting. Try to see this offer is a snapshot of the kinds of schools that might recruit your son. Start to explore other schools just like this one, a little better than this one, and a little worse and see what's out there.