There's a lot more difference between the wings than ailerons vs no ailerons. The increased dihedral of the 3-channel wing makes the rudder much more responsive and makes the plane positively roll-stable. This is important because if the plane gets our of shape you can just release the stick and the plane will roll upright by itself.
With the 4-channel wing the plane is a true sport plane, not suitable for beginners at all. It will not self-cancel a bank angle. Instead, to enter a turn you give a momentary aileron input and center the stick when you reach the desired bank angle. The plane will stay at that angle until you cancel the bank with opposite aileron. What actually turns the plane is the application of some up elevator while the plane is banked. This all sounds easy, but it is just too much to think about for a beginner if he doesn't have an instructor and a buddy box to save him when it all goes south.
What you have is the ideal learner setup. Start with the 3-channel wing, unplugging the rudder at the transmitter and plugging it into the aileron circuit. This puts your primary roll control on your right stick, just as it will be for 4-channel operation.
Learn to fly the plane well in 3-channel. When you are solid, and you will know when you are, strap on the aileron wing, moving the rudder to the rudder circuit and plugging in the ailerons. You are now flying a plane that you are very comfortable with and the only change is ailerons. Instead of having to learn all the habits of a new plane you can concentrate on learning just the ailerons.
And then it's a true sport flier. It will be fun for years!
If you don't have the brushless power option your brushed motor won't last a long time. When it gives up the ghost (sooner, not later) you would be way ahead of the game to buy the brushless power upgrade. Batteries last longer, the motor has indefinite lifespan and your power will triple.