need help choosing shields and parts for a robot

I'm working on a project that basically amounts to using an iPhone as the core of a robot. However, I want to use Arduino for the robot's body. So think of an iPhone walking around strapped to a rover body. The idea is:

As it stands, my main doubts are about the following items from the list:

4: Which servos should I get?

5: All in all, I need to control 4 DCs and 2 servos. Is there any shield that can do this and communicate with the Arduino via I2C? Cause I've seen Dargu's own motor shield for the chassis I'm considering, and it'll drive the 4 DCs and provide feedback back in for the encoders but it uses the PWM from Arduino and a bunch of pins. If I used this for instance, I then would still need a separate shield for the extra 2 servos. On the other hand, I've seen an Adafruit shield that communicates via I2C and can drive 4 DCs, steppers or servos: Adafruit Motor/Stepper/Servo Shield for Arduino v2 Kit [v2.3] : ID 1438 : $19.95 : Adafruit Industries, Unique & fun DIY electronics and kits. In this case I'd need 2 of them still (I have 4 DCs + 2 servos) but at least they can be stacked in the I2C bus. The one thing is, what would I do about the "wheel" motors' encoders in this case?

7: What Arduino would do for this whole project in your opinion?

8: What should I do about the power supply for this whole thing? (excluding the iPhone). Basically, something that would allow the iPhone Frankenstein a couple to a few hours of autonomy powering the Arduino, BLE and motor shields.