Do yo want the minimum number or what works best?
1/2, 1/3, and 2/5 games all use a minimal number of $1 chips with the $5 chip the "workhorse" chip. You can easily run a full table of any of these games with a rack of $1s, or 10 chips/player. You will need enough $20 or $25 chips to fill out the set and $100s (if used) to cover re-buys.
Minimal:
100 x $1
300 x $5
100 x $25 ($20)
$100 bills for the rest - That's a $4100 bank ($3600 if using $20 chips) , which lets 10 players buy in for $400+ each. That will get you started and is only 500 chips.
Better:
100 x $1
600 x $5
200 x $25 ($20)
100 x $100 - 1000 chips, a $18,000 bank ($17,000 if using $20 chips), which covers anything short of a very vigorous 2/5 game.
Best:
Go to 200 x $1, 300 x $25 ($20), and fill in the rest with $5s. Lots of them. Add more high denomination chips if you really have room. 1500+ chips and you can spread 2 tables of any of these stakes.
Lastly, my recommendation for these games is $25 chips. It's what your players will be used to. Someone on PCF said that if you rebuy in increments of $20, you should use a $20 chip. If you rebuy in increments of $100 (like the games you want to spread), then go with a $25. This is a hot topic, but I agree with that advice.