Hi I’m making one of those rhythm dance games you see in arcades and I wanted it to be usable to plug and play at home through my computer with arduino Leonardo. One concern for this project would be if I would be able to power enough of those 5v WS2812B LEDs to light up when buttons are pressed. I’m not familiar at all with arduino capabilities when it comes to power and I don’t want to break anything so any advice is appreciated.
You may have some misunderstanding here.
The Arduino is not in any respect whatsoever, a power supply. It does not "power" anything.
To power 5 V WS2812 ("NeoPixel)" LED strips you use a 5 V power supply. For up to 2.1 Amps, a USB "Phone Charger" is often a very convenient and inexpensive supply for up to 35 WS2812 LEDs as well as your Arduino.
You will need to connect the 5 V directly to your LEDs and also to the Arduino. You can connect 5 V to the "5V" pin on the Leonardo except when you have it connected to the PC via USB. You could connect the 5 V to the Arduino via the USB connector but you must connect the 5 V separately to the LED strip. 
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I want the power to come from the pc when plugged in usb. So the most leds that light up is 35 with this method? Are there ways to go more? Let’s say lower brightness or something like that
Bad idea!
I referred to a USB "Phone Charger", not a PC. For the USB output of a PC, it is eight WS2812 LEDs.
The risk of saying you will only use partial brightness, is that you might set them to full. 
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What would be the recommended approach to make this work? The goal is to be able to use the arduino as a controller with input strokes using ezbutton library and have a set of leds light up with the button being hit.
You can use an external 5V PSU to power the LEDs while the Leonardo is powered by the PC/USB. Just don't connect the 5V line from the PSU to the Leonardo, only connect the grounds.
Do you have a Leonardo yet? If not, buy a Pro Micro instead, much more practical. Do not confuse Pro Micro with Pro Mini
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So the led will be connected through the 5v of psu and the ground will go to arduino which will allow them to register when signals are read from the buttons, which in this case the buttons are based on a simple design of 2 contacts meshing together to give a signal to the pins I have labeled and I already have the Leonardo unfortunately.
As I explained in the last paragraph of #2. 
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Gotcha and can one psu power 2 arduino’s connected leds ?
Woah! 2 Arduinos? Why?
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The reason for 2 is because i made the dance platforms separated as a player 1 player 2 design this allows me to be flexible with wiring and encasing everything within, and moving it around or storing it if im not using (each platform measures at 3ft by 4ft ). So thats why i ask if i am able to use LEDs with both, would it be possible to use one power supply if im cautious with how many leds i use in total? @PaulRB @Paul_B
So the 2 Arduino are connected to 2 USB ports and the PC software treats them as 2 separate devices?
I guess that could be ok. Mostly, beginners believe they need to use 2 Arduino in the same project for the wrong reasons, making the project more difficult than it needs to be. In you project, I don't know, perhaps that is the best way.
Yes, you can use the same PSU. Use as many LEDs as you need but be sure that the PSU has capacity for all the LEDs that may be on at a single time, and be sure to have a common ground between both Arduino and both sets of LEDs.
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