very interesting project.
One thing you should consider very carefully is how to interface each of your sensors.
With out extra circutry you have 6 analog inputs and it seems that you are going to use them up for the flex sensores.
The two preassure sensors are analog sensores too and will need 2 analog inputs, so you need a way to expand the number of analog inputs onthe Arduino board. This is not very difficult, check the playground for how to use the 4051 analog multiplexor IC.
The compass uses 12C that should not be a problem.
The FTDI Viniculum chip can interface serially if my memory serves me.
I think the complexity in this project wil come from the many different ways you are going to interface to your sensors.
Mulitplexed analog input from flex and preassure sensors.
I2C for the compass
Serial for the FTDI
But i think it is possible.
So what you are missing is a way to use more than 6 analog inputs. A method is described in the playground here:
http://www.arduino.cc/playground/Learning/4051
Good luck