Before making any commitment, you and your son should make sure you get very clear definition of what he is saying... this coach may be solid as a rock but what exactly does it mean "you have a spot on my team"? And what parameters will be in place for him to receive the $6K the following year? This is one area where it is OK for parent to be part of the discussion because you are likely footing a good portion of the bill.
There are countless stories of these types of conversations getting very lost in translation or over time. It is very easy to get really excited about first real interest. Take your time and keep asking questions. And do not let your son take the "one at a time" approach. Shotgun all the way!
How good is the fit with this school? How realistic is it to take pre-med and play ball at this school? ...at any school he might attend? Is son reaching out directly to a list of schools or is he relying on being seen at events?