1738Dad,
Congrats! That is a great first offer. It sounds like you've made a list and visited a bunch of schools. You have a feel for this and you know more than you think. Letting other schools "directly" know he has an offer is a personal choice. My son was not comfortable with that, but he let his travel coach and high school leak that information to other interested programs. That approach worked for us.
A long time coach with a winning program says a lot. So those are added positives.
So, my next questions would turn to academic fit and financial fit. What does your son want to study and what is that academic program like at this school? Is it good enough, good or excellent? Also, after your son talks to the RC or Academic Liason about the academic side of the house, I'd request or reach out to a Financial Aid officer. There may be additional programs and financial benefits available to your son if he posts a great SAT/ACT score to go along with his GPA...he is only a sophomore. One school my son was considering had a Presidential scholarship available but there were strings attached. Again, this is all about getting a lot of information in a short period of time.
One more thing that you need to find out is how long is the offer good for. When my son received his first offer it was not time bound. However, a few weeks later a time deadline was applied when the RC found out that another school offered, and he was visiting another school. This looks like a sincere offer on their part. Good luck, and take as much time as you need to feel comfortable or not comfortable with it is my best advice!
As always, JMO.