re: What to do w/ $500,000

Several have given you good advice.

Keep your 3% mortgage. Don't pay extra on it.

Pay extra on student loans to reduce or eliminate. Paying off in full depends on what you would do with that amount of money. Opportunity cost of money is real, but 6.5% isn't cheap these days.

Once you are in position to buy a vehicle with cash, you can do that for life with proper discipline. Save/invest for the next vehicle ahead of time.

Knowing you expect to move in a few years, it sure is nice to be able to buy a house without being contingent on selling old house for a down payment. Reduces stress. Can get you the house if ever in a multiple offer situation. So have some liquid assets at that time.