The 9 channel Futaba you have does a pretty good job with mixes. Yes you can try the setup as you intend first. I recommend performing the little test I mention above to check how the surfaces will do in flight.

For sports planes I often rely upon the TX for mixes, but for my larger 3D planes I use the syncronizers for better accuracy.

And yes that servo is fine for all of the surfaces, particularly at 6v.

Because of the faster servo response at the higher voltage, I use a 6v supply on my Funtana.