If that's all the hardware you are going to use, then you can hook up your buttons directly to digital pins and do the same for the 8 outputs, or you can use a shift register for them. This will reduce the complexity and the overhead. Also, I suggest that you start on a smaller scale; for instance, with just 2 buttons (like you seem to have done already) and 2 relays, or even 2 simple LEDs to emulate what you want the relays to do.
But one issue remains, and it is of importance, so don't overlook it: what on earth do you want your prototype to do? What behaviour are you after? And, last but not least, what have you tried?