Four channel is fixed pitch, lift is regulated by the gass handle.
With collective pitch, lift is mostly regulated by the angle of the rotor blades.
For the later, you need a more expensive remote and chopper.
The benefit is that you have constant power available. If you want lift, you just turn the blades, and the full power, of the already rotating rotor, is available. With collective pitch, you can even fly upside down by simply rotating the blades to the right angle. This can’t be done with 4 channel fixed pitch models.
But, to start, four channels is ok, I guess.