7.2VDC and 6VDC power supply from 12V transformer
If full-wave rectify your 12V transformer and filter it you'll get around 15VDC. You could use 3 pieces of your DC-DC converter to give you 5.5V at 5A  (2 servo) + 5A (2 servo) + 4.5A (1 servo and 2 small servo) and use an LM7809 to preregulate for the Arduino. 

The total consumption is more than 80W peak, so you could also split the supply using 2x 50VA transformers. 

So- two 50VA transformers, two bridge rectifiers, two large filter capacitors, 3 DC-DC converters, and one LM7809 (with input and output capacitors). Using 4 DC-DC converters would allow you to split the load between the transformers more evenly, but probably okay as is. Capacitor value- maybe 22000uF/25V for about 1.5V ripple p-p.