Automatic Alcohol Dispenser: What is the Resistor's value for transistor?

I wanted to assemble the circuit below

Link: https://www.instructables.com/id/DIY-Automatic-Alcohol-Dispenser-No-Arduino-Needed/

I read about the transistor’s datasheet and I found out that the current base is -3A max rating. These are my following questions:

1. Why does it need a 1k ohm resistor? Since voltage is only 5v
2. What would happen if I remove the 1k ohm resistor?
3. How to compute the value of the resistor for the transistor’s base? I saw formulas in google but still confuses me.

Your answer and explanation is gladly appreciated. Thanks