I actually moved from 3 channel planes to 4 channel with a modified mode one set up on a T-28. I put the ailerons on the left stick with the throttle, and had rudder and elevator on the right stick. It made the transition and learning to use the ailerons easy because I could fly the T-28 ok and get to altitude with just elevator and rudder like I was used to, then I played with the ailerons using the left stick (which I hadn't been used to flying with other than for throttle).
I think my rolls, loops, and inverted flying were easier and more prescise that way, but things like knife edges, flat spins, and stall turns were harder. I don't know why, probably just me.
I also had previously done, and still do, some full scale flying. Mode 2 is more like full scale control than mode one.
I do believe if I had to do it over, I would just go ahead and start with mode 2. Just my opinion