Help?!? PC Fan, control and tachometer

Hi all-
This is a message from a father in need! My son is creating a science fair project using Arduino. Of course we are running out of time before the due date, and we are extreme novices using Arduino.
Any help provided would be a life saver.

He would like to measure rpm needed to lift various objects, ping pong ball etc. Almost like a wind tunnel but vertical.
I’ve spent many hours trying to find a project out there that combines all the themes in one but haven’t had much luck. I’ve found many sources for measuring rpm but am now struggling to find a way to control rpm of a fan.
Here’s how far I’ve gotten, trying to sketch out the easiest, cheapest way to accomplish his goal.

Fan: Considering using a 4 pin pc fan so I can use the 3rd pin to read the rpm and the 4th to control the speed. (Remember we are novices, so apologies if that is not quite right)

If I am able to use the pc fan to read the rpm, terrific, now I need to know how to use the Uno to read the rpm preferably with an lcd read out.
Again with the pc fan, I have no idea how to control the speed. It doesn’t necessarily need to be with the Arduino for this project but if possible how?
Also, I am concerned that the fan will require too much power and will kill the Arduino. How do I power the fan separately but still read the rpm with the Arduino?

If not a pc fan what? I’m considering using a Dremel with a rotor attached so at least I can control the speed with the Dremel switch.

Thanks in advance for any help.
If we accomplish our goal I promise I will figure out how to submit this project here and elsewhere for other people to use as a guide.

Hi and welcome.

So you have an idea about what components to use, and now you can't find any examples about how to do what you want to do ?

I don't know how to read the fan speed of a standard PC fan.
But i'm sure you can find out by asking Google.
Next is to do that using an Arduino.

Controlling the fan speed, i suppose that is done by a PWM signal.
It doesn't matter what you are controlling using PWM, it's all the same from the Arduino's point of view.

Displaying values on a LCD isn't too hard.

You can find a lot of examples about these things, it will be up to the two of you to combine that to a working sketch that does what you like it to do.
It takes time, sure.
But the both of you will learn form doing this yourself.
Don't get me wrong, there's tons of people who would like to help out explaining some question.
But the both of you have to put in some effort yourself.
Just don't ask people to do the work for you (not telling you that's what you are doing now).
You don't want to teach your kid to have others do his job for him, right ?
So ask specific questions about your project.

Find the Learning button on the top bar of this forum, and the different sections that will help you.
You can find out about LCD displays, and controlling some motors by PWM.
There's a lot you could have found that way in the 2 hours this thread exists at this moment.