Welcome to FF.
Not to sound like your Dad or some old curmudgeon, but your best bet to prepare your path is to forget the big tracks for now.
Use that as an ultimate goal.
Autocross is the best place to start.
A lot of people will "poo poo" AX as an entry into road or closed circuit racing, but it is not.
AX teaches you a lot about yourself as a driver and the car you drive. Initially, the only person you have to beat is yourself. You are racing against the clock. Everything that happens on a road course is compressed into HALF the time on an AX course.
As a result, you are applying skills that you have to execute in a timely and deliberate fashion with AX. On a road course, you have time to think about it. This is not always a good thing. The more time you have to think, the more opportunity you have to second guess yourself. Eventually, with AX, things become second nature and muscle memory takes over.
The other thing is that in AX, everything you do translates directly to the big tracks and the street. With a road course, this is not always the case.
There is an old expression, that you may have seen before, that pretty well sums it up.
"Good autocrossers make GREAT road racers. Great road racers make LOUSY autocrossers."
The last thing, being that you are only 16, is the issue of expense. You can go to an AX and basically "run what you brung". The only additional equipment you need to get started is a tire pressure gauge and access to an air pump at a gas station.
Set your tire psi for 10 psi over stock and drive. Be sure to return to street pressures on the way home.
Don't worry about modifications or race tires for at least your first year in the sport. You may not win a lot of events, but the experience you gain will pay off tremendously in the coming years as you advance your career.
I would recommend that you AX for 2 full seasons before trying a road course (especially one like Laguna Seca) and go from there.
It's GREAT to see that you are interested in trying out legal and sanctioned racing. Make heavy use of the expertise at your local AX and then at road courses as you become comfortable in that environment.
There are people with natural ability, I am not one of those people, but we can all learn. So, pay attention to the gray beards, listen to their advice, and use your youth and enthusiasm to go far.
Good luck and remember that there are a number of experienced drivers on this forum that can provide perspective.