Bugs, Paul's article is a good guide to selecting the type of financial planner that is a stockbroker. Before your son signs on with a stockbroker/financial planner, he should form a relationship with a personal finance financial planner who helps him plan his personal finances and investment strategies. This kind of financial advisor doesn't sell anything. Instead, he charges by the hour or on a flat fee to review the client's situation and establish a plan for him. This would include evaluations like your immediate question of whether to pay off student loans, when is a mortgage vs buying outright makes sense, etc. In addition, a personal financial advisor would help deciding asset allocation, Roth IRA vs 401(k) selection, tax strategies, insurance needs, tax strategies, etc. A stockbroker will tell you he can do these things but they really don't have the expertise. And your son shouldn't trust investment and personal financial strategies to anyone who earns a commission selling anything. Think of a personal financial planner as the transmission that allows your son to put all of his financial engine's power directly onto the road.
Once he gets his strategy in order he will be ready to establish a relationship with someone at a brokerage house who can supervise his investments. He should keep meeting with his financial advisor (not stock broker) at least twice a year to review his asset allocation and again at the end of the year for tax planning. If he does this, he may find he has little need for an investment advisor and that he doesn't need to pay anyone to tell him to balance his investments in three or four index funds.
Here is a short article on the different names 'financial planners" use and what is the real difference in what they do. I would really encourage him to see a fee-based financial counselor before doing any specific investments.
https://www.forbes.com/sites/feeonlyplanner/2012/03/15/the-difference-between-a-stockbroker-financial-advisor-and-planner-explained/?sh=4917bf52981a