IMO for a cash game the first thing* you need to figure out (or agree on with your group) is the blind level. I assume you are playing 50¢/$1.00 blinds. Is that right? Because if you are playing $1/$2 or 25¢/50¢ then the chip answers would be different.
Second is buy-in. For a 50¢/$1 game, $100 would be the typical buy-in. And rebuys of any amount up to $100 that they have left in their pocket after you take their original buy-in.

Decide whether they can re-buy only when they bust out, or when they get down to some level (like $30-$50).
Then you can decide on starting stack of chips, and extra chips for re-buys.
For a 50¢/$1 game, you should have 25¢ or 50¢ chips. Assuming you have 50¢ chips, I would start each person with something like this:
- 10 x 50¢ (not too many, since they're only used for blinds. If you only have 25¢ chips, use 12-20)
- 30 x $1
- 13 x $5
That's a big stack of 53 chips.
For re-buys, I would not give out any more 50¢ chips, but mostly $5 chips or with 1-2 $25s. After someone re-buys, let them get change at the table from another player -- there will be lots of $1s and 50¢ on the table.
Good luck and have some fun!
* I guess the real first thing is which game you are playing. I'm assuming No Limit Hold 'em. If it is Limit, then the chip stacks/denoms will change.