CNBTR12mm Silver GA12-N20 15RPM Miniature Metal Electric 3V DC Gear Motor Gearwheel with 10mm Output Shaft Set of 5

Q: Could this handle 3.3V? I want to use it with my Arduino

I just use double A batteries. It's a runs slower.

Q: what size screw is used for mounting the motor with the top plate holes?

The screws marked 1.4 in this kit worked great: https://a.co/d/9TxUXAN -or- https://www.amazon.com/dp/B01N07NN0K Note: I purchased motors 3 yrs ago so I guess there is a small chance the screw details have changed but doubt it.

Q: Does it come soldered to wires?

The picture doesn't show any and the ones I received did not have wires attached.

Q: Can I change the direction of the rotation? If so, how?

Simply change the polarity of the battery connection. I’m doing that in a rotating display device using a SPDT toggle switch with center off. Wire the the battery to the center terminals. Criss cross 2 wires to connect opposite sides of the outer terminals and wire the motor to one of the ends. When you toggle the switch one way, the rotation direction will be opposite that from the switch the other way. Slider switches are also available as DPDT