We've been through it a few times. He was drafted last spring, but returned to school for his junior year.
Doing a few questionnaires is exciting but it's really just scratching the surface. Questionnaires get sent to a lot of guys. Scouts are like recruiters, some are outwardly interested and seek an opportunity to get to know your son early on, others are more reserved until later in the process. You'll sometimes hear about kids drafted by scouts they claim they never talked to. That said, if scouts are really on him, it will likely be several and you will start regularly seeing them at games in the spring. The more interest, meaning the higher he's likely to go, the more scouts you will see more often. When you start seeing cross-checkers, national cross-checkers or perhaps members of the front office then you know he's going pretty high. In home visits and offers to come to team workouts at their location is often another part of the process.
You mention not being crazy about skipping college. Ultimately that decision may come down to money if interest heats up. If you don't know about slot values in the draft, Baseball America is a pretty good source. They list the slots for each position in the draft and then the actual signing bonus paid for each (most) draftees. The other thing to learn about is the scholarship program that you could negotiate in. That has it's own set of complexities.