Re: IO and supply pad
First of all it may not be right to compare the digital pads to analog pads as they have diverse requirements like voltage and current carrying capability.
From the standpoint of 1 input : 3 output, your arragement should work. However, why do you need more than 1 VDD node? If you need more current, then use opposite locations and join them (dont forget this step). Similarly, put two GND opposite and at max distance from VDD and of course, join them. If you have unused pads, then so be it. Dont fill up pad for the sake of using it. Finally, make sure that you are using the chip area prudently.
I am not sure what is your circuit that you are building, if I know something I can help better.
Let me know whether the above suggestion helped or not...
Srivats