Matt man..I am thinking 9 people probably generate quite a bit of food scraps. Do you have an outdoor compost pile? If so, you could start with a pound of worms and just go slow, not counting on the worms to dispose of all this OM for quite a while, as you wait for your population to grow. The extra food scraps could be added to your compost pile.
This is how I think about how many and how much (worms/food)..I think of surface area, 1 pound of worms per square ft, that would be fed a pound of food scraps a week. These are not hard fast numbers or amounts, just something to kind of wrap your brain around and see how it fits your situation. I do not think 1 plastic bin could handle the scraps from 9 people. I would opt, if possible, for an outdoor, in ground bin.

I wouldn't buy worms from a company that says their, or any, "worm starter" food will "get them growing to their full size quick and help fight diseases".

Chuckiebtoo

For what it's worth, considering the size of your family, you could start smaller, but I think you'd be best served by an 18 gallon (Approx) bin and 2lbs of worms.

Although I augment my worms food stock with cornmeal, bran, bread crumbs and alfalfa, I think paying premium prices for marketed "worm food" is silly as you can create your own for much less. Frankly, assuming regular food of fruit and veggie waste, worms can do just fine.

I also question the marketing hype regarding any feed stock that prevents diseases. Growth is one thing but preventing disease claims frankly seems like foolishness that can't be backed up and makes me think of snake oil !