I can use like 8 tiny's or something
Yes you can, I helped a mate do just this albeit with only 4 slave processors.
OTOH if there are chips designed for this they may be a better option.
Now the next thing to think about is how often do you need the data to be sampled? Can you just sample one motor at a time then move onto the next one and sample that? If so then all you need is a MUX.
Rob