Few Strip of WS2812 with 3V3
Your scheme should work OK if...


Fix your incorrect PNP transistor to be an NPN with emitter to GND. Putting the NPN in the signal path means that the signal from the MCU to the LED strings is logically inverted. You will have to account for that in the software that drives the pin.
Make sure the BUF and AND gate parts are powered from 5V so you get a full 0 - 5 V swing at their outputs.
Use a BUF chip that has an 74HCTxxx type part number so that the inputs work correctly with 3.3V swings despite the part operating at 5V.
Beware to only drive one of the BUF inputs high at a time.
Be aware that the NPN transistor may exhibit a non symmetrical propagation delay from low to high versus the high to low transitions. This will somewhat distort the timing pulses that you send to the WS2812's. This could be significant if you are trying to drive the signals to the LED strings at the upper end of its timing range. A fix for this could be to replace the NPN transistor with another 74HCTxxx buffer to get better operational speed. 
For that matter you could consider using a 74HCT08 gate and feed the 3.3V signals from the MCU directly into it and fully eliminate the transistor and BUF parts entirely.